GBE: use a uniform style to calculate register size for curbe allocation.

GBE: use a uniform style to calculate register size for curbe allocation.

Concentrate the register allocation to one place, and don't
use hard coded size when do curbe register allocation. All
register size allocation should use the same method.

Signed-off-by: Zhigang Gong <zhigang.gong@intel.com>
Reviewed-by: "Yang, Rong R" <rong.r.yang@intel.com>
Reviewed-by: "Song, Ruiling" <ruiling.song@intel.com>