PcAtChipsetPkg/IsaAcpiDxe: Restore PCI attributes correctly

PcAtChipsetPkg/IsaAcpiDxe: Restore PCI attributes correctly

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=405

The original code enables some BITs in PCI attributes in Start(),
but wrongly to disable these BITs in Stop().

The correct behavior is to save the original PCI attributes before
enables some BITs in Start(), and restore to original value
in Stop().

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>