video/backlight: LM3630A needs PWM

The LM3630A driver cannot be successfully built if we don't
enable the PWM subsystem. This patch makes that dependency
explicit in Kconfig and prevents broken randconfig builds.

Based on Arnd Bergmann patch but split out into seperate
commits per driver based on feedback.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
Acked-by: Jingoo Han <jg1.han@samsung.com>
Acked-by: Bryan Wu <cooloney@gmail.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/video/backlight/Kconfig

@@ -370,7 +370,7 @@ config BACKLIGHT_AAT2870
 
 config BACKLIGHT_LM3630A
 	tristate "Backlight Driver for LM3630A"
-	depends on BACKLIGHT_CLASS_DEVICE && I2C
+	depends on BACKLIGHT_CLASS_DEVICE && I2C && PWM
 	select REGMAP_I2C
 	help
 	  This supports TI LM3630A Backlight Driver