Sync patch r15576 from main trunk.
PcAtChipsetPkg: Enable timer interrupt through I/O APIC.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jeff Fan <jeff.fan@intel.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/branches/UDK2014@15579 6f19259b-4bc3-4df7-8a09-765794883524