gbm: Add buffer handling and visuals for fp16 formats

Define and set a new loader cap DRI_LOADER_CAP_FP16, indicating that gbm can
handle fp16 formats.

Signed-off-by: Kevin Strasser <kevin.strasser@intel.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>

include/GL/internal/dri_interface.h

@@ -1100,6 +1100,7 @@ enum dri_loader_cap {
     * only BGRA ordering can be exposed.
     */
    DRI_LOADER_CAP_RGBA_ORDERING,
+   DRI_LOADER_CAP_FP16,
 };
 
 struct __DRIdri2LoaderExtensionRec {