[ARM] 4479/1: AT91: Define new MMC register bits

Add definitions for RDPROOF, WRPROOF and PDCFBYTE bits of the Mode
Register in the updated MMC controller found on the AT91SAM9260 and
AT91SAM9263 processors.

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