OvmfPkg: PciHostBridgeLib: install 64-bit PCI host aperture

OvmfPkg: PciHostBridgeLib: install 64-bit PCI host aperture

On the normal boot path (which is when PciHostBridgeDxe runs), the PCDs
have been calculated; report the 64-bit PCI host aperture to
PciHostBridgeDxe.

In the Ia32 build, the PCD values (zeros) come directly from the DEC file,
and this patch makes no difference.

Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Marcel Apfelbaum <marcel@redhat.com>
Cc: Thomas Lamprecht <t.lamprecht@proxmox.com>
Ref: https://github.com/tianocore/edk2/issues/59
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>