drm/of: add helper to count data-lanes on a remote endpoint

drm/of: add helper to count data-lanes on a remote endpoint

If the DSI panel supports versatile lanes configuration, its driver
might require determining the number of DSI data lanes, which is usually
specified on the DSI host side of the OF graph. Add new helper as a
pair to drm_of_get_data_lanes_count_ep() that lets callers determine
number of data-lanes on the remote side of the OF graph.

Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patch.msgid.link/20260413-waveshare-dsi-touch-v3-6-3aeb53022c32@oss.qualcomm.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>