drm/fourcc: Add missing half-float formats

drm/fourcc: Add missing half-float formats

Not something that is likely to be scanned out, but GPUs usually support
half-float formats with 1, 2, or possibly 3 components, and it is useful
to be able to import/export them with a valid fourcc, and/or use gbm to
create them.

These correspond to PIPE_FORMAT_{R16,R16G16,R16G16B16}_FLOAT in mesa.

Signed-off-by: Rob Clark <robin.clark@oss.qualcomm.com>
Acked-by: Simona Vetter <simona@ffwll.ch>
Acked-by: Daniel Stone <daniels@collabora.com>
Link: https://lore.kernel.org/r/20250625173712.116446-2-robin.clark@oss.qualcomm.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>