UefiCpuPkg: Define AMD Memory Encryption specific CPUID and MSR

The patch defines AMD's Memory Encryption Information CPUID leaf and SEV
status MSR. The complete description for CPUID leaf is available in APM
volume 2, Section 15.34.

Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Jeff Fan <jeff.fan@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Leo Duran <leo.duran@amd.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Reviewed-by: Jeff Fan <jeff.fan@intel.com>