ChibiOS upgrade: Filter 'all' builds by platform

[tzarc]

Description

Adds support for building all keyboards, filtered by platform key.
Examples:

make all:default             # as before
make all-avr:default         # only build AVR-based keyboards
make all-chibios:default     # only build ChibiOS keyboards
make all-arm_atsam:default   # only build arm_atsam-based keyboards

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout/userspace (addition or update)
• Documentation

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• 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.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).

[drashna]

/me makes board named "chibios" just to troll tzarc
/s

:D

sounds like a good idea!

[tzarc]

Prefixed all target names with all-.