hook-functions: Don't add backlight modules if we have generic fb device

If we have a generic framebuffer device then there should be no
need to set up any backlight in early boot.

Also, backlight devices are sometimes handled by large drm drivers
like i915 which we don't want to include by default.

Fixes: da851903 ("hook-functions: Include modules for Chromebook ...")
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

hook-functions

@@ -466,7 +466,7 @@ dep_add_modules()
 	fi
 
 	# sys walk some important device classes
-	for class in backlight extcon gpio phy pwm regulator rtc; do
+	for class in extcon gpio phy pwm regulator rtc; do
 		class_add_modules "$class"
 	done
 
@@ -501,6 +501,7 @@ dep_add_modules()
 	done
 
 	if [ "$walk_graphics" = "yes" ]; then
+		class_add_modules backlight
 		class_add_modules graphics
 	fi