Implement sampler support.

Implement sampler support.

Accept sampler kernel argument and pass the sampler to driver side.
At driver side, gen7 driver will allocate a sampler slot and initlaize
one sampler state according to the cl sampler state. and then pass
back the slot index to the curbe array.

After this commit, read_imagei(image, sampler, coord) could work as
expected.

Signed-off-by: Zhigang Gong <zhigang.gong@linux.intel.com>
Reviewed-by: Lu Guanqun <guanqun.lu@intel.com>