drm/i915: remove pre_pll_enable hook from DDI/gen9+ crtc enable

The hook was added to cater for DSI, but with the hooks rearranged on
the DSI encoder side, this is no longer needed. It was a bit silly
anyway to have two hooks called back-to-back.
Reviewed-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1448619706-21293-2-git-send-email-jani.nikula@intel.com

drivers/gpu/drm/i915/intel_display.c

@@ -4981,8 +4981,6 @@ static void haswell_crtc_enable(struct drm_crtc *crtc)
 
 	intel_set_cpu_fifo_underrun_reporting(dev_priv, pipe, true);
 	for_each_encoder_on_crtc(dev, crtc, encoder) {
-		if (encoder->pre_pll_enable)
-			encoder->pre_pll_enable(encoder);
 		if (encoder->pre_enable)
 			encoder->pre_enable(encoder);
 	}