OvmfPkg/VirtioPciDeviceDxe: 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 () ->
    MemoryAllocationLib.AllocatePages()

- VIRTIO_DEVICE_PROTOCOL.FreeSharedPages () ->
    MemoryAllocationLib.FreePages ()

- VIRTIO_DEVICE_PROTOCOL.MapSharedBuffer () -> no-op

- VIRTIO_DEVICE_PROTOCOL.UnmapSharedBuffer () -> no-op

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>

OvmfPkg/VirtioPciDeviceDxe/VirtioPciDevice.h

@@ -3,6 +3,7 @@
   Internal definitions for the VirtIo PCI Device driver
 
   Copyright (C) 2013, ARM Ltd
+  Copyright (c) 2017, AMD Inc, All rights reserved.<BR>
 
   This program and the accompanying materials are licensed and made available
   under the terms and conditions of the BSD License which accompanies this
@@ -156,4 +157,37 @@ VirtioPciSetDeviceStatus (
   IN  UINT8                          DeviceStatus
   );
 
+EFI_STATUS
+EFIAPI
+VirtioPciAllocateSharedPages (
+  IN  VIRTIO_DEVICE_PROTOCOL        *This,
+  IN  UINTN                         NumPages,
+  OUT VOID                          **HostAddress
+  );
+
+VOID
+EFIAPI
+VirtioPciFreeSharedPages (
+  IN  VIRTIO_DEVICE_PROTOCOL        *This,
+  IN  UINTN                         NumPages,
+  IN  VOID                          *HostAddress
+  );
+
+EFI_STATUS
+EFIAPI
+VirtioPciMapSharedBuffer (
+  IN      VIRTIO_DEVICE_PROTOCOL        *This,
+  IN      VIRTIO_MAP_OPERATION          Operation,
+  IN      VOID                          *HostAddress,
+  IN OUT  UINTN                         *NumberOfBytes,
+  OUT     EFI_PHYSICAL_ADDRESS          *DeviceAddress,
+  OUT     VOID                          **Mapping
+  );
+
+EFI_STATUS
+EFIAPI
+VirtioPciUnmapSharedBuffer (
+  IN  VIRTIO_DEVICE_PROTOCOL        *This,
+  IN  VOID                          *Mapping
+  );
 #endif // _VIRTIO_PCI_DEVICE_DXE_H_