OvmfPkg: Add Tdx measurement data structure in WorkArea

OvmfPkg: Add Tdx measurement data structure in WorkArea

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=4243

From the perspective of security any external input should be measured
and extended to some registers (TPM PCRs or TDX RTMR registers).

There are below 2 external input in a Td guest:
 - TdHob
 - Configuration FV (CFV)

TdHob contains the resource information passed from VMM, such as
unaccepted memory region. CFV contains the configurations, such as
secure boot variables.

TdHob and CFV should be measured and extended to RTMRs before they're
consumed. TdHob is consumed in the very early stage of boot process.
At that moment the memory service is not ready. Cfv is consumed in
PlatformPei to initialize the EmuVariableNvStore. To make the
implementation simple and clean, these 2 external input are measured
and extended to RTMRs in SEC phase. That is to say the tdx measurement
is only supported in SEC phase.

After the measurement the hash values are stored in WorkArea. Then after
the Hob service is available, these 2 measurement values are retrieved
and GuidHobs for these 2 tdx measurements are generated.

This patch defines the structure of TDX_MEASUREMENTS_DATA in
SEC_TDX_WORK_AREA to store above 2 tdx measurements. It can be extended
to store more tdx measurements if needed in the future.

Cc: Erdem Aktas <erdemaktas@google.com>
Cc: James Bottomley <jejb@linux.ibm.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Michael Roth <michael.roth@amd.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>