OvmfPkg: Update Sec to support Tdx

OvmfPkg: Update Sec to support Tdx

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

There are below major changes in this commit.

1. SecEntry.nasm
In TDX BSP and APs goes to the same entry point in SecEntry.nasm.

BSP initialize the temporary stack and then jumps to SecMain, just as
legacy Ovmf does.

APs spin in a modified mailbox loop using initial mailbox structure.
Its structure defition is in OvmfPkg/Include/IndustryStandard/IntelTdx.h.
APs wait for command to see if the command is for me. If so execute the
command.

2. Sec/SecMain.c
When host VMM create the Td guest, the system memory informations are
stored in TdHob, which is a memory region described in Tdx metadata.
The system memory region in TdHob should be accepted before it can be
accessed. So the major task of this patch is to process the TdHobList
to accept the memory. After that TDVF follow the standard OVMF flow
and jump to PEI phase.

PcdUse1GPageTable is set to FALSE by default in OvmfPkgX64.dsc. It gives
no chance for Intel TDX to support 1G page table. To support 1G page
table this PCD is set to TRUE in OvmfPkgX64.dsc.

TDX_GUEST_SUPPORTED is defined in OvmfPkgX64.dsc. This macro wraps the
Tdx specific code.

TDX only works on X64, so the code is only valid in X64 arch.

Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Jordan Justen <jordan.l.justen@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: Jiewen Yao <jiewen.yao@intel.com>
Signed-off-by: Min Xu <min.m.xu@intel.com>