drm/rockchip: add drm_connector_helper_funcs.mode_valid callback

This function is not optionally.  It gets called in
drm_helper_probe_single_connector_modes() at boot to validate the modes
filled in by ->get_modes().

Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>

Change-Id: I6053ea6570a09c1acc64a3bcc651a3eabef0af06
drm/rockchip: remove drm_mode_connector_detach_encoder

This function was removed upstream in commit:

 69fa5293bf8d0ade3fd726848c7af925227e9180
 drm/kms: rip out drm_mode_connector_detach_encoder

Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>

Change-Id: I0e2628b4d0c2c6d0d34e5af01391ceb1a22d2f99
drm/rockchip: fix code style