Init Support for Family SAML21

[sabas1080]

Hi I have started the port for the SAML family

so far the UF2 file can be generated, but

• the flag -nostartfiles must be removed in Makefiles
• I can't test hardware until next week

I wait for your feedback, thanks

fixes #82

[mmoskal]

Let me know when you have tested on hardware!

[sabas1080]

@mmoskal tested in hardware and ok!