ArmVirtPkg/FdtPciHostBridgeLib: add MMIO64 support

ArmVirtPkg/FdtPciHostBridgeLib: add MMIO64 support

If the pci-host-ecam-generic DT node describes a 64-bit MMIO region,
account for it in the PCI_ROOT_BRIDGE description that we return to
the generic PciHostBridgeDxe implementation, which will be able to
allocate BARs from it without any further changes.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Ref: https://tianocore.acgmultimedia.com/show_bug.cgi?id=65