Add support for SAMD51 series?

[deanm1278]

Hello! The team here at Adafruit has a line boards based on the new SAMD51 chip. Would it be ok if I created a pull request adding the SAMD51 CMSIS files? CMSIS files for other devices would not be changed.

[facchinm]

Hi @deanm1278 , no problem in updating CMSIS, we only need to take extra care to avoid issues like arduino/ArduinoCore-samd#214 (the DEFINE meaning was changed without changing its name). Feel free to propose a PR if you wish to speedup the process!

[deanm1278]

Great! I have proposed this PR #8
it provides support for samd51 line without interfering with existing CMSIS files

[cmaglie]

Further discussion on #8.