Since the LoongArch SPEC has adjusted the CSR 0x20 register name and
the MdePkg also added the new name, so enable it in UefiCpuPkg.
Cc: Ray Ni <ray.ni@intel.com>
Cc: Rahul Kumar <rahul1.kumar@intel.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Jiaxin Wu <jiaxin.wu@intel.com>
Signed-off-by: Chao Li <lichao@loongson.cn>