Expose configs when allow_fp16_configs has been enabled and DRI_LOADER_CAP_FP16 is set in the loader. Also, define a new dri configuration option so users can disable exposure of fp16 formats. Make fp16 opt-in for i965. Signed-off-by: Kevin Strasser <kevin.strasser@intel.com> Reviewed-by: Adam Jackson <ajax@redhat.com> Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>