[RTC] rtc-sa1100: remove dependence on asm/rtc.h

Move the two functions rtc-sa1100 wants from the old ARM RTC library
into the rtc-sa1100 driver.

Acked-by: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>