UefiCpuPkg: Update AESNI support checking logic

UefiCpuPkg: Update AESNI support checking logic

With correct model CPU, current checking logic will
always execute AsmReadMsr64 operation and then check
ECX.AESNI[bit 25] = 1. Update checking logic to check
ECX.AESNI[bit 25] = 1 first and then do AsmReadMsr64
operation.

Cc: Eric Dong <eric.dong@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Bell Song <binx.song@intel.com>
Reviewed-by: Eric Dong <eric.dong@intel.com>