Runtime: disable some unecessary image formats.
Runtime: disable some unecessary image formats.

Per OpenCL, the minimum list of supported format is as below:
CL_RGBA:
  CL_UNORM_INT8
  CL_UNORM_INT16
  CL_SIGNED_INT8
  CL_SIGNED_INT16
  CL_SIGNED_INT32
  CL_UNSIGNED_INT8
  CL_UNSIGNED_INT16
  CL_UNSIGNED_INT32
  CL_HALF_FLOAT
  CL_FLOAT

CL_BGRA:
  CL_UNORM_INT8

Let's only support this type and CL_R currently.

Also removed an unnecessary assertion. And fix the CL_Rx's type size.

Signed-off-by: Zhigang Gong <e04a7b9b70b1e4c6318cf117dcd1a9056e14b97a@linux.intel.com>
Reviewed-by: He Junyan <8f73a735c668918c9613b750d3a88ebf2489599f@inbox.com>

wdv4758h/beignet,freedesktop-unofficial-mirror/beignet,zhenyw/beignet,freedesktop-unofficial-mirror/beignet,freedesktop-unofficial-mirror/beignet,zhenyw/beignet,freedesktop-unofficial-mirror/beignet,ignatenkobrain/beignet,wdv4758h/beignet,wdv4758h/beignet,zhenyw/beignet,ignatenkobrain/beignet,ignatenkobrain/beignet,wdv4758h/beignet,zhenyw/beignet,ignatenkobrain/beignet,wdv4758h/beignet,ignatenkobrain/beignet,zhenyw/beignet