sam: can: CAN driver for SAM0 socs

Driver was based on can_sam. SAMC21 has only 1 interrupt for one
can "output", so can interrupt has to executes two lines of
interrupts.
CAN is configured to use OSC48M clock via GLCK7. GLCK7 is set
by divider configured from dts.

Signed-off-by: Kamil Serwus <kserwus@gmail.com>