drm/i915: Fix cap check for intel_dp_aux_backlight driver

intel_dp_aux_backlight driver should check for the
DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP before enable the driver.
Signed-off-by: Puthikorn Voravootivat <puthik@chromium.org>
Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170511230225.142870-2-puthik@chromium.org

drivers/gpu/drm/i915/intel_dp_aux_backlight.c

@@ -144,6 +144,7 @@ intel_dp_aux_display_control_capable(struct intel_connector *connector)
 	 */
 	if (intel_dp->edp_dpcd[1] & DP_EDP_TCON_BACKLIGHT_ADJUSTMENT_CAP &&
 	    (intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP) &&
+	    (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP) &&
 	    !((intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_PIN_ENABLE_CAP) ||
 	      (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_PWM_PIN_CAP))) {
 		DRM_DEBUG_KMS("AUX Backlight Control Supported!\n");