[ARM] 4421/1: AT91: Value of _KEY fields.

Use the actual value (0xA5) for the AT91_SHDW_KEY and AT91_WDT_KEY
register fields instead of a bitmask.

This is consistent with how AT91_RSTC_KEY is defined, and is easier to
use in code.

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