OMAPDSS: cleanup dss_recheck_connections further

Cleanup dss_recheck_connections, move and rename it to a static
dss_init_connections function inside display.c. Improve the function to
return errors, and implement a matching dss_uninit_connections that can
be used to free the mgr->dssdev link.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>