MdePkg: Add TdxLib to wrap Tdx operations

RFC: https://bugzilla.tianocore.org/show_bug.cgi?id=3429

TdxLib is created with functions to perform the related Tdx operation.
This includes functions for:
 - TdAcceptPages   : Accept pending private pages and initialize the pages
                     to all-0 using the TD ephemeral private key.
 - TdExtendRtmr    : Extend measurement to one of the RTMR registers.
 - TdSharedPageMask: Get the Td guest shared page mask which indicates it
                     is a Shared or Private page.
 - TdMaxVCpuNum    : Get the maximum number of virtual CPUs.
 - TdVCpuNum       : Get the number of virtual CPUs.

Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>
Cc: Zhiguang Liu <zhiguang.liu@intel.com>
Cc: Brijesh Singh <brijesh.singh@amd.com>
Cc: Erdem Aktas <erdemaktas@google.com>
Cc: James Bottomley <jejb@linux.ibm.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>
Signed-off-by: Min Xu <min.m.xu@intel.com>

MdePkg/Library/TdxLib/TdxLibNull.c

@@ -0,0 +1,106 @@
+/** @file
+
+  Null stub of TdxLib
+
+  Copyright (c) 2021, Intel Corporation. All rights reserved.<BR>
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+
+**/
+
+#include <Uefi/UefiBaseType.h>
+#include <Library/TdxLib.h>
+
+/**
+  This function accepts a pending private page, and initialize the page to
+  all-0 using the TD ephemeral private key.
+
+  @param[in]  StartAddress     Guest physical address of the private page
+                               to accept.
+  @param[in]  NumberOfPages    Number of the pages to be accepted.
+  @param[in]  PageSize         GPA page size. Accept 1G/2M/4K page size.
+
+  @return EFI_SUCCESS
+**/
+EFI_STATUS
+EFIAPI
+TdAcceptPages (
+  IN UINT64  StartAddress,
+  IN UINT64  NumberOfPages,
+  IN UINT32  PageSize
+  )
+{
+  return EFI_UNSUPPORTED;
+}
+
+/**
+  This function extends one of the RTMR measurement register
+  in TDCS with the provided extension data in memory.
+  RTMR extending supports SHA384 which length is 48 bytes.
+
+  @param[in]  Data      Point to the data to be extended
+  @param[in]  DataLen   Length of the data. Must be 48
+  @param[in]  Index     RTMR index
+
+  @return EFI_SUCCESS
+  @return EFI_INVALID_PARAMETER
+  @return EFI_DEVICE_ERROR
+
+**/
+EFI_STATUS
+EFIAPI
+TdExtendRtmr (
+  IN  UINT32  *Data,
+  IN  UINT32  DataLen,
+  IN  UINT8   Index
+  )
+{
+  return EFI_UNSUPPORTED;
+}
+
+/**
+  This function gets the Td guest shared page mask.
+
+  The guest indicates if a page is shared using the Guest Physical Address
+  (GPA) Shared (S) bit. If the GPA Width(GPAW) is 48, the S-bit is bit-47.
+  If the GPAW is 52, the S-bit is bit-51.
+
+  @return Shared page bit mask
+**/
+UINT64
+EFIAPI
+TdSharedPageMask (
+  VOID
+  )
+{
+  return 0;
+}
+
+/**
+  This function gets the maximum number of Virtual CPUs that are usable for
+  Td Guest.
+
+  @return maximum Virtual CPUs number
+**/
+UINT32
+EFIAPI
+TdMaxVCpuNum (
+  VOID
+  )
+{
+  return 0;
+}
+
+/**
+  This function gets the number of Virtual CPUs that are usable for Td
+  Guest.
+
+  @return Virtual CPUs number
+**/
+UINT32
+EFIAPI
+TdVCpuNum (
+  VOID
+  )
+{
+  return 0;
+}