[ARM] 3975/1: AT91: Comments in atmel_serial.h

Updated some of the comments in the atmel_serial.h header detailing
which bits are only available on the AT91RM9200 or the AT91SAM9xx
processors.

Signed-off-by: Andrew Victor <andrew@sanpeople.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
1 file changed