[WATCHDOG] SAM9 watchdog - supported on all SAM9 and CAP9 processors

The SAM9 watchdog driver is usable on the whole family of AT91SAM9 and
CAP9 processors.
Update the configuration to indicate this and allow the driver to be selected.

Signed-off-by: Andrew Victor <linux@maxim.org.za>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>