drm/doc: Integrate drm_modes.c kerneldoc

And clean it up so that there's no kerneldoc warnings. There's still a
lot to do with this one here.

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

diff --cc Documentation/DocBook/drm.tmpl
Simple merge

diff --cc drivers/gpu/drm/drm_modes.c
Simple merge