drm/tilcd: select BACKLIGHT_LCD_SUPPORT

The dependecies for BACKLIGHT_CLASS_DEVICE are defined a bit
strange, but it seems one has to always select both BACKLIGHT_CLASS_DEVICE
and BACKLIGHT_LCD_SUPPORT to avoid this error:

drivers/gpu/drm/tilcdc/tilcdc_panel.c:396:
undefined reference to `of_find_backlight_by_node'

Cc: Rob Clark <[e-mail]>
Cc: [e-mail]
Cc: Dave Airlie <[e-mail]>
Signed-off-by: Arnd Bergmann <[e-mail]>
Signed-off-by: Dave Airlie <[e-mail]>

drivers/gpu/drm/tilcdc/Kconfig

···
 	select DRM_GEM_CMA_HELPER
 	select VIDEOMODE_HELPERS
 	select BACKLIGHT_CLASS_DEVICE
+	select BACKLIGHT_LCD_SUPPORT
 	help
 	  Choose this option if you have an TI SoC with LCDC display
 	  controller, for example AM33xx in beagle-bone, DA8xx, or