OvmfPkg/Virtio10Dxe: implement IOMMU-like member functions

OvmfPkg/Virtio10Dxe: implement IOMMU-like member functions

The patch implements the newly added IOMMU-like member functions by
respectively delegating the job to:

- VIRTIO_DEVICE_PROTOCOL.AllocateSharedPages() ->
    EFI_PCI_IO_PROTOCOL.AllocateBuffer()

- VIRTIO_DEVICE_PROTOCOL.FreeSharedPages() ->
    EFI_PCI_IO_PROTOCOL.FreeBuffer()

- VIRTIO_DEVICE_PROTOCOL.MapSharedBuffer() ->
    EFI_PCI_IO_PROTOCOL.Map()

- VIRTIO_DEVICE_PROTOCOL.UnmapSharedBuffer() ->
    EFI_PCI_IO_PROTOCOL.Unmap()

Suggested-by: Laszlo Ersek <lersek@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Regression-tested-by: Laszlo Ersek <lersek@redhat.com>