linux-imx

drm/doc: Improve docs for conn_state->best_encoder

It's mandatory and considered core state since ioctls rely on this
working.

Thanks to Laurent for pointing out this gap.

v2: Clarify to "atomic drivers" only.

Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Sean Paul <sean@poorly.run>
Acked-by: Sean Paul <sean@poorly.run>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190506144629.5976-1-daniel.vetter@ffwll.ch