Initialize alarm register in PcRtc module entrypoint to make UEFI SCT GetWakeupTime pass.

(Sync patch r16425 from main trunk.)

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Elvin Li <elvin.li@intel.com>
Reviewed-by: Feng Tian <feng.tian@intel.com>
Reviewed-by: Eric Jin <eric.jin@intel.com>

git-svn-id: svn://svn.code.sf.net/p/edk2/code/branches/UDK2014.SP1/PcAtChipsetPkg@16459 6f19259b-4bc3-4df7-8a09-765794883524