UefiCpuPkg: Enable Tdx support in MpInitLib

UefiCpuPkg: Enable Tdx support in MpInitLib

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

In TDVF BSP and APs are simplified. BSP is the vCPU-0, while the others
are treated as APs.

So MP intialization is rather simple. ApWorker is not supported, BSP is
always the working processor, while the APs are just in a
wait-for-precedure state.

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: Eric Dong <eric.dong@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Rahul Kumar <rahul1.kumar@intel.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Ray Ni <ray.ni@intel.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>
Signed-off-by: Min Xu <min.m.xu@intel.com>