video: exynos_fb: configure backlight GPIOs if specified in DT

Add support to configure PWM_OUT(PWM output) GPIO and
BL_EN(backlight enable) GPIO, if provided in FIMD DT node.

Signed-off-by: Ajay Kumar <ajaykumar.rs@samsung.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>
diff --git a/doc/device-tree-bindings/video/exynos-fb.txt b/doc/device-tree-bindings/video/exynos-fb.txt
index dc4e44f..b022f61 100644
--- a/doc/device-tree-bindings/video/exynos-fb.txt
+++ b/doc/device-tree-bindings/video/exynos-fb.txt
@@ -61,6 +61,8 @@
 				disabled with compatible string
 				"samsung,sysmmu-v3.3", with a "reg" property
 				holding the register address of FIMD sysmmu.
+	samsung,pwm-out-gpio: PWM output GPIO.
+	samsung,bl-en-gpio: backlight enable GPIO.
 
 Example:
 SOC specific part: