OvmfPkg/OvmfPkg.dec: Add 8259-related PCDs in OVMF DEC file

OvmfPkg/OvmfPkg.dec: Add 8259-related PCDs in OVMF DEC file

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

According to the DEC file in PcAtChipsetPkg, this commit adds the two
8259-driver-related PCDs into the OvmfPkg DEC file.

Please note that, instead of adding the two PCDs under section:
[PcdsFixedAtBuild, PcdsDynamic, PcdsDynamicEx, PcdsPatchableInModule]

as in PcAtChipsetPkg.dec file, they are added in section:
[PcdsFixedAtBuild]

in OvmfPkg.dec instead.

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>