UefiCpuPkg/PiSmmCpuDxeSmm: Enable NXE if it's supported

UefiCpuPkg/PiSmmCpuDxeSmm: Enable NXE if it's supported

If PcdDxeNxMemoryProtectionPolicy is set to enable protection for memory
of EfiBootServicesCode, EfiConventionalMemory, the BIOS will hang at a page
fault exception triggered by PiSmmCpuDxeSmm.

The root cause is that PiSmmCpuDxeSmm will access default SMM RAM starting
at 0x30000 which is marked as non-executable, but NX feature was not
enabled during SMM initialization. Accessing memory which has invalid
attributes set will cause page fault exception. This patch fixes it by
checking NX capability in cpuid and enable NXE in EFER MSR if it's
available.

Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Jian J Wang <jian.j.wang@intel.com>
Reviewed-by: Eric Dong <eric.dong@intel.com>