drm/rockchip: Drop drm_driver.load/unload callbacks

They are deprecated and by moving their implementations to bind/unbind
we can call drm_connector_register_all instead of open-coding it.

Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1465557253-10670-1-git-send-email-tomeu.vizoso@collabora.com