drm/i915: Don't register CRT connector when DDI E can't be used

On HSW/BDW DDI A and E share 2 lanes, so when DDI A requires the
shared lanes DDI E can't be used. The lanes are not supposed to
be dynamically switched between the two uses, so there's no point
in registering the CRT connector when DDI E has no lanes.

v2: Fix typos in the commit message (Paulo)

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1449005396-15319-1-git-send-email-ville.syrjala@linux.intel.com

drivers/gpu/drm/i915/intel_display.c

@@ -14260,6 +14260,10 @@ static bool intel_crt_present(struct drm_device *dev)
 	if (HAS_PCH_LPT_H(dev) && I915_READ(SFUSE_STRAP) & SFUSE_STRAP_CRT_DISABLED)
 		return false;
 
+	/* DDI E can't be used if DDI A requires 4 lanes */
+	if (HAS_DDI(dev) && I915_READ(DDI_BUF_CTL(PORT_A)) & DDI_A_4_LANES)
+		return false;
+
 	if (IS_VALLEYVIEW(dev) && !dev_priv->vbt.int_crt_support)
 		return false;