OvmfPkg: add library class BlobVerifierLib with null implementation

BlobVerifierLib will be used to verify blobs fetching them from QEMU's
firmware config (fw_cfg) in platforms that enable such verification.

The null implementation BlobVerifierLibNull treats all blobs as valid.

Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Ashish Kalra <ashish.kalra@amd.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: Min Xu <min.m.xu@intel.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=3457
Signed-off-by: Dov Murik <dovmurik@linux.ibm.com>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>

OvmfPkg/Library/BlobVerifierLibNull/BlobVerifierLibNull.inf

@@ -0,0 +1,24 @@
+## @file
+#
+#  Null implementation of the blob verifier library.
+#
+#  Copyright (C) 2021, IBM Corp
+#
+#  SPDX-License-Identifier: BSD-2-Clause-Patent
+#
+##
+
+[Defines]
+  INF_VERSION                    = 1.29
+  BASE_NAME                      = BlobVerifierLibNull
+  FILE_GUID                      = b1b5533e-e01a-43bb-9e54-414f00ca036e
+  MODULE_TYPE                    = BASE
+  VERSION_STRING                 = 1.0
+  LIBRARY_CLASS                  = BlobVerifierLib
+
+[Sources]
+  BlobVerifierNull.c
+
+[Packages]
+  MdePkg/MdePkg.dec
+  OvmfPkg/OvmfPkg.dec