OvmfPkg: Update DSC/FDF files to consume 8259/8254 drivers in OvmfPkg

REF:https://bugzilla.tianocore.org/show_bug.cgi?id=1496

This commit updates the OVMF DSC/FDF files to consume the copied
8259InterruptControllerDxe and 8254TimerDxe drivers within OvmfPkg.

The unconsumed PCD:
gPcAtChipsetPkgTokenSpaceGuid.Pcd8259LegacyModeEdgeLevel

is removed from DSC files as well.

Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Ray Ni <ray.ni@intel.com>
Signed-off-by: Hao Wu <hao.a.wu@intel.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>