ArmVirtPkg: Enable CpuMmio2Dxe

CpuMmio2Dxe is supports MMIO, enable it.

Build-tested only (with "ArmVirtQemu.dsc").

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=4584

Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Leif Lindholm <quic_llindhol@quicinc.com>
Cc: Sami Mujawar <sami.mujawar@arm.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Chao Li <lichao@loongson.cn>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>

ArmVirtPkg/ArmVirtQemuKernel.dsc

@@ -431,7 +431,7 @@
   #
   # PCI support
   #
-  ArmPkg/Drivers/ArmPciCpuIo2Dxe/ArmPciCpuIo2Dxe.inf {
+  UefiCpuPkg/CpuMmio2Dxe/CpuMmio2Dxe.inf {
     <LibraryClasses>
       NULL|OvmfPkg/Fdt/FdtPciPcdProducerLib/FdtPciPcdProducerLib.inf
   }