OvmfPkg: fix gPcAtChipsetPkgTokenSpaceGuid build break

OvmfPkg: fix gPcAtChipsetPkgTokenSpaceGuid build break

In OvmfPkgIa32X64.dsc:

Paraphrasing svn rev 13350: gPcAtChipsetPkgTokenSpaceGuid is declared in
PcAtChipsetPkg.dec and used via AcpiPlatformDxe.inf, but with the latest
build tools, since this package builds multiple architectures (IA32 & X64)
and AcpiPlatformDxe is used on X64 only, it is now necessary to place the
gPcAtChipsetPkgTokenSpaceGuid PCD's in the [PcdsFixedAtBuild.X64] section.

In the two other .dsc files:

Make a similar change to keep file contents more easily comparable.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
[jordan.l.justen@intel.com: change all .dsc files to keep them diffable]
Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@13724 6f19259b-4bc3-4df7-8a09-765794883524