OvmfPkg X64 ResetVector: Move page tables from 512KB to 8MB

OvmfPkg X64 ResetVector: Move page tables from 512KB to 8MB

To help consolidate OVMF fixed memory uses, we declare this
range in MEMFD and thereby move it to 8MB.

We also now declare the table range in the FDF to set
PCDs. This allows us to ASSERT that CR3 is set as expected
in OVMF SEC.

OvmfPkgIa32.fdf and OvmfPkgIa32X64.fdf are updated simply
for consistency.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@15146 6f19259b-4bc3-4df7-8a09-765794883524