UefiCpuPkg/MpInitLib: Skip reading PlatformId on AMD processors.

UefiCpuPkg/MpInitLib: Skip reading PlatformId on AMD processors.

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=2556

This patch uses CPUID signature check to skip reading the PlatformId MSR,
which is not implemented on AMD processors.

The PlatformId is used for loading microcode patches, which is also not
supported and AMD-based platforms. To mitigate the PlatformId dependency,
PcdCpuMicrocodePatchAddress and PcdCpuMicrodePatchRegionSize must be set
to 0 (default value), in order to bypass microcode loading code paths.

Cc: Eric Dong <eric.dong@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Leo Duran <leo.duran@amd.com>
Reviewed-by: Ray Ni <ray.ni@intel.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>