Add target STM32F767 Nucleo

[networkfusion]

Description

This adds a port for the target STM32F767ZI Nucleo for ChibiOS.
Although aligns to the datasheet, most hardware devices have not been tested.
Readme requires updating but left out as it is likely this board should be a community target.

Motivation and Context

Improves the boards supported.

How Has This Been Tested?

The board is seen by VS and runs nanoCLR.

Screenshots

Types of changes

• Improvement (non-breaking change that improves a feature, code or algorithm)
• Bug fix (non-breaking change which fixes an issue with code or algorithm)
• New feature (non-breaking change which adds functionality to code)
• Breaking change (fix or feature that would cause existing functionality to change)
• Config and build (change in the configuration and build system, has no impact on code or features)
• Dev Containers (changes related with Dev Containers, has no impact on code or features)
• Dependencies (update dependencies and changes associated, has no impact on code or features)
• Documentation (changes or updates in the documentation, has no impact on code or features)

Checklist

• My code follows the code style of this project (only if there are changes in source code).
• My changes require an update to the documentation (there are changes that require the docs website to be updated).
• I have updated the documentation accordingly (the changes require an update on the docs in this repo).
• I have read the CONTRIBUTING document.
• I have tested everything locally and all new and existing tests passed (only if there are changes in source code).

[Ellerbach]

Nice work!

[Ellerbach]

why have you commented fully both onewire files?

[networkfusion]

It causes too many issues in my experience. See nanoframework/Home#1270

[networkfusion]

Split into #2804 and nanoframework/nf-Community-Targets#226