rtc: fixes and new functionality for fm3130

- add sanity check for alarm data in fm3130_probe

- fix fm3130_set_alarm.

  According to the datasheet, setting match bit '0' indicates that the
  corresponding alarm field will be used in the match process

- add operation alarm_irq_enable operation which is responsible for
  handling RTC_AIE_ON, RTC_AIE_OFF ioctls

- remove clearing of AF bit after reading rtc/alarm control register:
  according to datasheet this bit is cleared anyway when rtc/alarm control
  register is read

[akpm@linux-foundation.org: make fm3130_alarm_irq_enable() static, fix comment layout]
Signed-off-by: Sergey Matyukevich <geomatsi@gmail.com>
Acked-by: Wan ZongShun <mcuos.com@gmail.com>
Acked-by: Sergey Lapin <slapin@ossfans.org>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>