drm/i915: Parse panel backlight controller from VBT

Currently the backlight controller is taken as 0. It needs to derive
value from the VBT. Adding the necessary changes.

v2 by Jani:
 - drop obsolete comments, drop redundant initialization (Bob)
 - merge debug logging into one

Signed-off-by: Uma Shankar <uma.shankar@intel.com>
Signed-off-by: Vidya Srinivas <vidya.srinivas@intel.com>
Reviewed-by: Bob Paauwe <bob.j.paauwe@intel.com>
Tested-by: Bob Paauwe <bob.j.paauwe@intel.com>
Tested-by: Mika Kahola <mika.kahola@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1481189178-426-1-git-send-email-jani.nikula@intel.com
diff --git a/drivers/gpu/drm/i915/intel_bios.c b/drivers/gpu/drm/i915/intel_bios.c
index eaade27..1cf2fa6 100644
--- a/drivers/gpu/drm/i915/intel_bios.c
+++ b/drivers/gpu/drm/i915/intel_bios.c
@@ -330,17 +330,19 @@ parse_lfp_backlight(struct drm_i915_private *dev_priv,
 
 		method = &backlight_data->backlight_control[panel_type];
 		dev_priv->vbt.backlight.type = method->type;
+		dev_priv->vbt.backlight.controller = method->controller;
 	}
 
 	dev_priv->vbt.backlight.pwm_freq_hz = entry->pwm_freq_hz;
 	dev_priv->vbt.backlight.active_low_pwm = entry->active_low_pwm;
 	dev_priv->vbt.backlight.min_brightness = entry->min_brightness;
 	DRM_DEBUG_KMS("VBT backlight PWM modulation frequency %u Hz, "
-		      "active %s, min brightness %u, level %u\n",
+		      "active %s, min brightness %u, level %u, controller %u\n",
 		      dev_priv->vbt.backlight.pwm_freq_hz,
 		      dev_priv->vbt.backlight.active_low_pwm ? "low" : "high",
 		      dev_priv->vbt.backlight.min_brightness,
-		      backlight_data->level[panel_type]);
+		      backlight_data->level[panel_type],
+		      dev_priv->vbt.backlight.controller);
 }
 
 /* Try to find sdvo panel data */