OvmfPkg/AmdSev/SecretPei: build hob for full page

Round up the size of the SEV launch secret area to a whole page, as
required by BuildMemoryAllocationHob.  This will allow the secret
area defined in the MEMFD to take less than a whole 4KB page.

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: Brijesh Singh <brijesh.singh@amd.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>

OvmfPkg/AmdSev/SecretPei/SecretPei.c

@@ -4,6 +4,7 @@
   Copyright (C) 2020 James Bottomley, IBM Corporation.
   SPDX-License-Identifier: BSD-2-Clause-Patent
 **/
+#include <Base.h>
 #include <PiPei.h>
 #include <Library/HobLib.h>
 #include <Library/PcdLib.h>
@@ -17,7 +18,7 @@ InitializeSecretPei (
 {
   BuildMemoryAllocationHob (
     PcdGet32 (PcdSevLaunchSecretBase),
-    PcdGet32 (PcdSevLaunchSecretSize),
+    ALIGN_VALUE (PcdGet32 (PcdSevLaunchSecretSize), EFI_PAGE_SIZE),
     EfiBootServicesData
     );