Update Ethernet support

[AdrianSoundy]

Description

Add support for boards that have a GPIO pin that switches the PHY power
Currently enabled by defines.

Removed some old test code.

TODO : Have some header file to have board specific configuration data in so we can have ESP32 community targets.

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]

This looks like a board configuration and quite "static" so a good place would be target_common.h.in.

Unless it makes more sense to have it as a build options... not enterely sure about that...

[josesimoes]

LGTM!