drm: of: forbid bridge-only calls to drm_of_find_panel_or_bridge()

drm: of: forbid bridge-only calls to drm_of_find_panel_or_bridge()

Up to now drm_of_find_panel_or_bridge() can be called with a bridge pointer
only, a panel pointer only, or both a bridge and a panel pointers. The
logic to handle all the three cases is somewhat complex to read however.

Now all bridge-only callers have been converted to
of_drm_get_bridge_by_endpoint(), which is simpler and handles bridge
refcounting. So forbid new bridge-only users by mandating a non-NULL panel
pointer in the docs and in the sanity checks along with a warning.

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Link: https://patch.msgid.link/20260511-drm-bridge-alloc-getput-panel_or_bridge-v6-11-f61c9e498b3f@bootlin.com
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>