watchdog: MAX63XX_WATCHDOG does not depend on ARM

Remove the ARM Kconfig dependency since the Maxim MAX63xx devices are
architecture independent.

Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>