UefiCpuPkg/Include/Register/Msr/SkylakeMsr.h: Add new MSR name and keep old one.

UefiCpuPkg/Include/Register/Msr/SkylakeMsr.h: Add new MSR name and keep old one.

Changes includes:
  1. Change MSR name:
    1. MSR_SKYLAKE_SGXOWNER0 => MSR_SKYLAKE_SGXOWNEREPOCH0
    2. MSR_SKYLAKE_SGXOWNER1 => MSR_SKYLAKE_SGXOWNEREPOCH1
  2. Keep old MSR definition(MSR_SKYLAKE_SGXOWNER0/1) for compatibility
    1. Use below coding style to define old MSR
         #define MSR_SKYLAKE_SGXOWNER0  MSR_SKYLAKE_SGXOWNEREPOCH0

Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Eric Dong <eric.dong@intel.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>
Acked-by: Laszlo Ersek <lersek@redhat.com>