drm/i915: Fix VLV PLL LPF coefficients for DAC

The current PLL settings produce a rather unstable picture when
I hook up a VLV to my HP ZR24w display via a VGA cable.

According to VLV2A0_DP_eDP_HDMI_DPIO_driver_vbios_notes_9, we should
use the the same LPF coefficients for DAC as we do for HDMI and RBR DP.
And indeed that seems to cure the shivers.

v2: Add the name of the relevant document to the commit message
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -4404,6 +4404,7 @@ static void vlv_update_pll(struct intel_crtc *crtc)
 
 	/* Set HBR and RBR LPF coefficients */
 	if (crtc->config.port_clock == 162000 ||
+	    intel_pipe_has_type(&crtc->base, INTEL_OUTPUT_ANALOG) ||
 	    intel_pipe_has_type(&crtc->base, INTEL_OUTPUT_HDMI))
 		vlv_dpio_write(dev_priv, DPIO_LFP_COEFF(pipe),
 				 0x005f0021);