PcAtChipsetPkg: Enable timer interrupt through I/O APIC

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Tycho Nightingale <tycho.nightingale@pluribusnetworks.com>
Reviewed-by: Elvin Li <elvin.li@intel.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@15576 6f19259b-4bc3-4df7-8a09-765794883524