drivers/rtc/rtc-rs5c372.c: add R2221T/L variant to the driver

Register layout is the same, so just add the variant to the appropriate
places.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Jan Luebbe <jlu@pengutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>