2021q3 release

This release covers everything from 2021-07-01 and has been tested with avr-gcc
v10.2.0 from Upstream and arm-none-eabi-gcc 10.3-2021.07 from Arm.

Breaking changes:

• STM32 EXTI configuration moved into separate modm:platform:exti module.
• STM32F3 ADC flags API made consistent with rest of ADC implementations.
• AVR SPI mode 1/2 was swapped.
• Interface SPI mode 3/4 was swapped.
• Configuration of CMSIS-DSP module is now done via <arm_math_local.h> file.

Features:

• STM32H7 support.
• SAMG55 support with USB and SPI drivers.
• SAMV70 support.
• STM32F1 ADC calibration.
• Adding silicon revision to modm:target option with /revN suffix.
• modm_initialize_platform() hook called right after startup.
• Strict IRQ name validation: Never wonder again why your IRQ isn't called!
• Much faster lbuild generation of modm:platform:gpio due to fewer files.
• New modm:platform:exti module for STM32 with optional IRQ handlers.

Integrated Projects:

• LVGL upgraded to v8.0.2.
• TinyUSB upgraded to v0.11.0.
• FreeRTOS upgraded to 202107.
• CMSIS-DSP upgraded to v5.8.0.

Fixes:

• Longer modm::delay_ms implementation.
• Lower C++ binary size due to not using atexit function.
• SPI mode 3/4 was swapped in interface, mode 1/2 swapped on AVR.
• Enable FPU in assembly before startup script.
• Fix inconsistent flags API for STM32F3 ADC.
• Refactored GpioConnector to remove template< Peripheral _ > signal
  boilerplate.

New development boards:

• NUCLEO-H743ZI as modm:board:nucleo-h743zi.
• NUCLEO-H723ZG as modm:board:nucleo-h723zg.
• Smart Response XE as modm:board:srxe.
• SAM G55 Xplained Pro as modm:board:samg55-xplained-pro.
• DevEBox STM32H750VB as modm:board:devebox-stm32h750vb.

New device drivers:

• ST7586S display as modm:driver:st7586s.

Known bugs:

• C++20 is not fully implemented by GCC10 yet, however modm does not use all
  features yet anyways. See #326.
• STM32F7: D-Cache not enabled by default. See #485.
• lbuild build and lbuild clean do not remove all previously generated files
  when the configuration changes. See #285.
• Generating modm on Windows creates paths with \ that are not compatible with
  Unix. See #310.
• arm-none-eabi-gdb TUI and GDBGUI interfaces are not supported on Windows.
  See #591.

Many thanks to all our contributors.
A special shoutout to first timers 🎉:

• Christopher Durand (@chris-durand)
• Daniel Krebs (@daniel-k)
• Henrik Hose (@hshose) 🎉
• Jakob Riepler (@XDjackieXD) 🎉
• Jeff McBride (@mcbridejc)
• Niklas Hauser (@salkinium)
• Thomas Sommer (@TomSaw)
• Tomasz Wasilczyk (@twasilczyk) 🎉
• Valeriy Osipov (@SgtPepperFTW) 🎉

PR #742 -> 2021q3.

Detailed changelog

2021-09-30: Upgrade CMSIS-DSP to v5.8.0

The :cmsis:dsp module options were removed in favor of letting the user
define them freely using a <arm_math_local.h> config file.

PR #742 -> 12bb41b.
Tested in hardware by @salkinium with medium impact on config.

2021-09-29: Refactor GPIO implementations

New implementation generates fewer files, which speeds up lbuild build
significantly for devices with many pins. EXTI implementation was moved into
its own module with an optional IRQ handler abstraction. Refactored signals
implementation to remove dragging around template< Peripheral _ > boilerplate.

PR #686 -> 30e24e6.
Tested in hardware by @salkinium with high impact on EXTI code.

2021-09-22: Add SAMV70 support

On custom hardware.

PR #681 -> 9036666.
Tested in hardware by @twasilczyk.

2021-09-17: Strict IRQ name validation

Validates MODM_ISR(name) at compile time to you never declare the wrong
IRQ that won't get called.

PR #685 -> 6057873.
Tested in hardware by @salkinium with low impact on MODM_ISR(name).

2021-09-16: Add DevEBox STM32H750VB board and example

PR #678 -> b4eddeb.
Tested in hardware by @hshose.

2021-09-10: Add SAMG55 SPI driver

PR #680 -> f4d5d6c.
Tested in hardware by @mcbridejc.

2021-09-09: Add SAMG55 USB driver via TinyUSB

PR #679 -> 93bba13.
Tested in hardware by @mcbridejc.

2021-09-09: Add SAMG55 support

Also adds SAM G55 Xplained Pro board and example.

PR #676 -> c148bf8.
Tested in hardware by @mcbridejc.

2021-09-07: Add ST7586S display driver

PR #673 -> 2c22fae.
Tested in hardware by @twasilczyk.

2021-08-23: Smart Response XE board and example

Adds support for the ATmega128RFA1 and the Smart Response XE board.

PR #669 -> a173bde.
Tested in hardware by @twasilczyk.

2021-07-15: Add STM32H7 support

Also adds NUCLEO-H743ZI and NUCLEO-H723ZG boards and examples.

PR #652 -> 80ed738.
Tested in hardware @chris-durand and @salkinium.