drm/i915: Toshiba CB35 has a controllable backlight

The Toshiba CB35 Chromebook (with Celeron 2955U CPU) has a controllable
backlight although its VBT reports otherwise. Apply quirk to ignore the
backlight presence check during backlight setup.

Patch tested by author on Toshiba CB35.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=79813
Signed-off-by: Scot Doyle <lkml14@scotdoyle.com>
CC: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Cc: stable@vger.kernel.org # 3.15 only
[danvet: Add cc: stable because the regressing commit is in 3.15.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -11670,6 +11670,9 @@ static struct intel_quirk intel_quirks[] = {
 
 	/* Acer C720 and C720P Chromebooks (Celeron 2955U) have backlights */
 	{ 0x0a06, 0x1025, 0x0a11, quirk_backlight_present },
+
+	/* Toshiba CB35 Chromebook (Celeron 2955U) */
+	{ 0x0a06, 0x1179, 0x0a88, quirk_backlight_present },
 };
 
 static void intel_init_quirks(struct drm_device *dev)