rtc: PCF50633 rtc driver

Signed-off-by: Balaji Rao <balajirrao@openmoko.org>
Cc: Andy Green <andy@openmoko.com>
Acked-by: Alessandro Zummo <a.zummo@towertech.it>
Cc: Paul Gortmaker <a.zummo@towertech.it>
Cc: rtc-linux@googlegroups.com
Signed-off-by: Samuel Ortiz <sameo@openedhand.com>