Same5x core compat clean

[crabel99]

Summary

Adds SAME5x compatibility support to the SAMD core paths by introducing a core compatibility shim and expanding existing SAMD51 feature gates to include the SAME51, SAME53, and SAME54 families.

What changed

• Added a SAME5x compatibility shim for mapping SAME5x CMSIS names onto the SAMD51-compatible core code paths.
• Expanded SAMD51-specific gates across the framework to include:
  • __SAME51__
  • __SAME53__
  • __SAME54__
• Updated affected core, USB, SERCOM, Wire, SPI, I2S, Servo, reset, timing, interrupt, and analog paths.
• Cleaned up remaining SAMD51-only gates in SPI, Wire, and SAMD_AnalogCorrection.
• Left SAMD21 behavior unchanged.

Validation

• Verified no remaining framework gates use __SAMD51__ without the corresponding SAME5x family checks.
• Ran git diff --check.
• Ran framework CI builds:
  • metro_m0: 24 succeeded, 0 failed, 37 skipped
  • metro_m4: 20 succeeded, 0 failed, 41 skipped