ARM: multi_v7_defconfig: enable backlight gpio

Enable generic GPIO based backlight driver.
Signed-off-by: Yannick Fertré <yannick.fertre@st.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>

arch/arm/configs/multi_v7_defconfig

@@ -641,6 +641,7 @@ CONFIG_FB_SIMPLE=y
 CONFIG_LCD_PLATFORM=m
 CONFIG_BACKLIGHT_PWM=y
 CONFIG_BACKLIGHT_AS3711=y
+CONFIG_BACKLIGHT_GPIO=y
 CONFIG_FRAMEBUFFER_CONSOLE=y
 CONFIG_FRAMEBUFFER_CONSOLE_ROTATION=y
 CONFIG_SOUND=m