drm: panel/sharp: add backlight dependency

The sharp panel code uses the backlight interface to
find a device, which fails when backlight is disabled:

drivers/built-in.o: In function `sharp_panel_probe':
:(.text+0x5ceac): undefined reference to `of_find_backlight_by_node'

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Dave Airlie <airlied@gmail.com>

drivers/gpu/drm/panel/Kconfig

@@ -31,6 +31,7 @@ config DRM_PANEL_SHARP_LQ101R1SX01
 	tristate "Sharp LQ101R1SX01 panel"
 	depends on OF
 	depends on DRM_MIPI_DSI
+	depends on BACKLIGHT_CLASS_DEVICE
 	help
 	  Say Y here if you want to enable support for Sharp LQ101R1SX01
 	  TFT-LCD modules. The panel has a 2560x1600 resolution and uses