Adds Atmel SAMC20 and SAMC21 soc. C series is based on Cortex-M0+.
C21 contains CAN interface.
The init routines are same for SAMC20 and SAMC21. They use one
clock OSC48M without configuration.
The code is inspirated from atmel_sam0/samd21.
Signed-off-by: Kamil Serwus <kserwus@gmail.com>
Kamil Serwus