watchdog: sa1100: use platform device registration

Rather than relying on machine specific headers to
pass down the reboot status and the register locations,
use resources and platform_data.

Aside from this, keep the changes to a minimum.

Cc: Wim Van Sebroeck <wim@linux-watchdog.org>
Cc: linux-watchdog@vger.kernel.org
Acked-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>