GBE: Refine the curbe entry allocation for sampler/image information.

GBE: Refine the curbe entry allocation for sampler/image information.

After the previous patch, we can move the image infomation curbe
entry allocation to prior to the instruction selection.

Then we can concentrate all curbe allocation before we do the
normal register allocation. This way can bring two advantages:
1. Avoid the image information curbe entry is allocated among the normal registers.
2. The register interval analyzing could handle the image/sampler information correctly.

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