Fix a size assert when setup bti.

Fix a size assert when setup bti.

Global constant buffer size is not align to 4 byte, will cause assert in BDW when set bti.
Per spec, the low two bits of surface state's width must be 11 if SURFACE_BUFFER's format is RAW.
Align the global constant buffer size to 4.

Signed-off-by: Yang Rong <rong.r.yang@intel.com>
Tested-by: "Meng, Mengmeng" <mengmeng.meng@intel.com>
Reviewed-by: Zhigang Gong <zhigang.gong@linux.intel.com>