drm/bridge: cdns-dsi: Drop crtc_* code

drm/bridge: cdns-dsi: Drop crtc_* code

With recent change the cdns_dsi_check_conf() is always called with
mode_valid_check = true. We can thus remove all the code related to the
"false" paths.

Tested-by: Parth Pancholi <parth.pancholi@toradex.com>
Tested-by: Jayesh Choudhary <j-choudhary@ti.com>
Reviewed-by: Devarsh Thakkar <devarsht@ti.com>
Link: https://lore.kernel.org/r/20250723-cdns-dsi-impro-v5-5-e61cc06074c2@ideasonboard.com
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>