drm: Fix plane type uabi breakage

drm: Fix plane type uabi breakage

Turns out assuming that only stuff in uabi is uabi is a bit naive, and
we have a bunch of properties for which the enum values are placed in
random headers. A proper fix would be to split out uapi include
headers, but meanwhile sprinkle at least some warning over them.

Fixes: 532b36712ddf ("drm/doc: Polish for drm_plane.[hc]")
Cc: Archit Taneja <[email protected]>
Cc: Sean Paul <[email protected]>
Reviewed-by: Jani Nikula <[email protected]>
Signed-off-by: Daniel Vetter <[email protected]>
Signed-off-by: Sean Paul <[email protected]>
Link: http://patchwork.freedesktop.org/patch/msgid/[email protected]