OvmfPkg: Create a calling area used to communicate with the SVSM

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=4654

An SVSM requires a calling area page whose address (CAA) is used by the
SVSM to communicate and process the SVSM request.

Add a pre-defined page area to the OvmfPkg and AmdSev packages and define
corresponding PCDs used to communicate the location and size of the area.
Keep the AmdSev package in sync with the OvmfPkg and adjust the AmdSev
launch and hash area memory locations.

Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Erdem Aktas <erdemaktas@google.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Michael Roth <michael.roth@amd.com>
Cc: Min Xu <min.m.xu@intel.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>

OvmfPkg/ResetVector/X64/OvmfSevMetadata.asm

@@ -2,7 +2,7 @@
 ; @file
 ; OVMF metadata for the AMD SEV confidential computing guests
 ;
-; Copyright (c) 2021, AMD Inc. All rights reserved.<BR>
+; Copyright (c) 2021 - 2024, AMD Inc. All rights reserved.<BR>
 ;
 ; SPDX-License-Identifier: BSD-2-Clause-Patent
 ;-----------------------------------------------------------------------------
@@ -26,6 +26,9 @@ BITS  64
 ;
 %define OVMF_SECTION_TYPE_CPUID           0x3
 
+; The SVSM Calling Area Address (CAA)
+%define OVMF_SECTION_TYPE_SVSM_CAA        0x4
+
 ; Kernel hashes section for measured direct boot
 %define OVMF_SECTION_TYPE_KERNEL_HASHES   0x10
 
@@ -67,6 +70,12 @@ CpuidSec:
   DD  CPUID_SIZE
   DD  OVMF_SECTION_TYPE_CPUID
 
+; SVSM CAA page
+SvsmCaa:
+  DD  SVSM_CAA_BASE
+  DD  SVSM_CAA_SIZE
+  DD  OVMF_SECTION_TYPE_SVSM_CAA
+
 %if (SEV_SNP_KERNEL_HASHES_BASE > 0)
 ; Kernel hashes for measured direct boot, or zero page if
 ; there are no kernel hashes / SEV secrets