drm/i915: move backlight enable later in vlv enable sequence

Follow-up to
commit 5004945f


Author: Jani Nikula <jani.nikula@intel.com>
Date:   Tue Jul 30 12:20:32 2013 +0300

    drm/i915: move encoder->enable callback later in VLV crtc enable

v2: Rebase on the renamed enable hooks, adding clarity (Ville)

Reference: http://mid.gmane.org/CAKMK7uFs9EMvMW8BnS24e5UNm1D7JrfVg3SD5SDFtVEamGfOOg@mail.gmail.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>