[ARM] 5109/1: Mark rtc sa1100 driver as wakeup source before registering it

Mark rtc sa1100 driver as wakeup source before registering it.
rtc_device_register evaluates device_can_wakeup(rtc->dev.parent) and
supresses the creation of /sys/class/rtc/rtcX/wakealarm if
device_can_wakeup is not (yet) true.

Signed-off-by: Uli Luckas <u.luckas@road.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>