IntelSiliconPkg/VTd: Refine VTd core driver

Refine the DRHD table print message.
Remove unused variable.

Hsd-es-id: 15012152545
Signed-off-by: Sheng Wei <w.sheng@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Rangasai V Chaganty <rangasai.v.chaganty@intel.com>
Cc: Jenny Huang <jenny.huang@intel.com>
Reviewed-by: Robert Kowalewski <robert.kowalewski@intel.com>