Adds Atmel SAMR21 soc which is based on SAMD21, but with a AT86RF233
radio connected internally via SPI.
The AT86RF233 is not yet supprted by Zephyr at this point.
This code is very much copy & paste from atmel_sam0/samd21
Signed-off-by: Benjamin Valentin <benpicco@googlemail.com>
Benjamin Valentin