rtc: pcf50633: manage RTC alarm "pending" flag

Add setting and clearing of the "pending" flag of the RTC alarm.  The
semantics follow the UEFI specification 2.2 available at
http://www.uefi.org/specs/

, i.e., the "pending" flag is cleared by
disabling the alarm, but not by any other condition (such as the passing
of time, a successful wakeup, or setting of a new alarm.)

Signed-off-by: Werner Almesberger <werner@openmoko.org>
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Paul Gortmaker <p_gortmaker@yahoo.com>
Cc: Balaji Rao <balajirrao@openmoko.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>