Make ChibiOS PAL interactions less STM32 specific

[zvecr]

Description

Coerce existing defines to hide STM32 context.

This then allows the concept to extend out to something like...

#if defined(HT32)
#    define PAL_MODE_ALTERNATE PAL_HT32_MODE_AF
#endif

And removing the need to litter the code base with various ifdefs.

Types of Changes

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

Issues Fixed or Closed by This PR

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]

Oh fun, this looks like it's breaking my planck EZ. rgb doesn't work on it, neither do the keys. Or even the front LEDs (they're left floating)