clvk has a conflict between what it exposes in CL_DEVICE_DOUBLE_FP_CONFIG and the cl_khr_fp64.

At the moment, cl_khr_fp64 is never exposed, while CL_DEVICE_DOUBLE_FP_CONFIG is not 0 when fp64 is supported.

I see two ways forward:

1. Always return 0 when CL_DEVICE_DOUBLE_FP_CONFIG is queried
2. Implement proper support for cl_khr_fp64:
   2.1 Expose cl_khr_fp64 when fp64 is supported
   2.2 Set CL_DEVICE_PREFERRED_VECTOR_WIDTH_DOUBLE and CL_DEVICE_NATIVE_VECTOR_WIDTH_DOUBLE to something else that 0 when fp64 is supported

I would prefer solution 1 because as cl_khr_fp64 is never exposed at the moment, it means that the CTS is not testing clvk on fp64. Enabling those tests would add lots of work to pass CTS in the future.