OvmfPkg/AmdSev: Expose the Sev Secret area using a configuration table

Now that the secret area is protected by a boot time HOB, extract its
location details into a configuration table referenced by
gSevLaunchSecretGuid so the boot loader or OS can locate it before a
call to ExitBootServices().

Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=3077
Signed-off-by: James Bottomley <jejb@linux.ibm.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Message-Id: <20201130202819.3910-7-jejb@linux.ibm.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@arm.com>
[lersek@redhat.com: fix indentation of InstallConfigurationTable() args]

OvmfPkg/AmdSev/SecretDxe/SecretDxe.inf

@@ -0,0 +1,37 @@
+## @file
+#  Sev Secret configuration Table installer
+#
+#  Copyright (C) 2020 James Bottomley, IBM Corporation.
+#
+#  SPDX-License-Identifier: BSD-2-Clause-Patent
+#
+##
+
+[Defines]
+  INF_VERSION                    = 0x00010005
+  BASE_NAME                      = SecretDxe
+  FILE_GUID                      = 6e2b9619-8810-4e9d-a177-d432bb9abeda
+  MODULE_TYPE                    = DXE_DRIVER
+  VERSION_STRING                 = 1.0
+  ENTRY_POINT                    = InitializeSecretDxe
+
+[Sources]
+  SecretDxe.c
+
+[Packages]
+  OvmfPkg/OvmfPkg.dec
+  MdePkg/MdePkg.dec
+
+[LibraryClasses]
+  UefiBootServicesTableLib
+  UefiDriverEntryPoint
+
+[Guids]
+  gSevLaunchSecretGuid
+
+[FixedPcd]
+  gUefiOvmfPkgTokenSpaceGuid.PcdSevLaunchSecretBase
+  gUefiOvmfPkgTokenSpaceGuid.PcdSevLaunchSecretSize
+
+[Depex]
+  TRUE