OvmfPkg: Add IntelTdxMetadata.asm

OvmfPkg: Add IntelTdxMetadata.asm

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

In TDX when host VMM creates a new guest TD, some initial set of
TD-private pages are added using the TDH.MEM.PAGE.ADD function. These
pages typically contain Virtual BIOS code and data along with some clear
pages for stacks and heap. In the meanwhile, some configuration data
need be measured by host VMM. Tdx Metadata is designed for this purpose
to indicate host VMM how to do the above tasks.

More detailed information of Metadata is in [TDVF] Section 11.

Tdx Metadata describes the information about the image for VMM use.
For example, the base address and length of the TdHob, Bfv, Cfv, etc.
The offset of the Metadata is stored in a GUID-ed structure which is
appended in the GUID-ed chain from a fixed GPA (0xffffffd0).

In this commit there are 2 new definitions of BFV & CFV.
Tdx Virtual Firmware (TDVF) includes one Firmware Volume (FV) known
as the Boot Firmware Volume (BFV). The FV format is defined in the
UEFI Platform Initialization (PI) spec. BFV includes all TDVF
components required during boot.

TDVF also include a configuration firmware volume (CFV) that is
separated from the BFV. The reason is because the CFV is measured in
RTMR, while the BFV is measured in MRTD.

In practice BFV is the code part of Ovmf image (OVMF_CODE.fd). CFV is
the vars part of Ovmf image (OVMF_VARS.fd).

Since AMD SEV has already defined some SEV specific memory region in
MEMFD. TDX re-uses some of the memory regions defined by SEV.
 - MailBox : PcdOvmfSecGhcbBackupBase|PcdOvmfSecGhcbBackupSize
 - TdHob   : PcdOvmfSecGhcbBase|PcdOvmfSecGhcbSize

[TDVF] https://software.intel.com/content/dam/develop/external/us/en/
documents/tdx-virtual-firmware-design-guide-rev-1.pdf

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