Update Managed heap allocator

[AdrianSoundy]

Description

Change to prepare for Spi Ram
Will attempt to allocate managed heap from SPI RAM ( Max size - 256K)
If not available ( current state ) it will allocate 64K from normal RAM as it does now.

How Has This Been Tested?

Tested with debugger to check working OK.
Tested Spi Ram with newer IDF libraries ( not ready yet )

Types of changes

• Improvement (non-breaking change that improves a feature, code or algorithm)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

Signed-off-by: adriansoundy <adriansoundy @gmail.com>

[nfbot]

Hi @AdrianSoundy,

I'm nanoFramework bot.
Thank you for your contribution!

A human will be reviewing it shortly. 😉

[josesimoes]

LGTM! making progresses as always!! 👏 👍