[SYCL][Bindless] Allow 3-channel image formats

[ProGTX]

This patch doesn't implement support for 3-channel formats, it just allows it in the spec and implementation so that a backend could implement it later (e.g. Level Zero).

• Removed check from image_descriptor::verify
• Updated spec to allow 3-channel formats
• Very simple test, just verifies that CUDA backend still fails
  • Missing some PTX intrinsics, use float4 instead of float4 when compiling for CUDA. The more important part is checking that the CUDA backend throws an exception when trying to create image.