ARM: imx_v6_v7_defconfig: Enable backlight gpio support.

The eukrea mbimxsd51 has a gpio backlight for its
  LCD display, so we turn that driver on.

Cc: Sascha Hauer <kernel@pengutronix.de>
Cc: linux-arm-kernel@lists.infradead.org
Cc: Fabio Estevam <fabio.estevam@freescale.com>
Cc: Eric Bénard <eric@eukrea.com>
Signed-off-by: NDenis Carikli <denis@eukrea.com>
Signed-off-by: NShawn Guo <shawn.guo@linaro.org>

arch/arm/configs/imx_v6_v7_defconfig

@@ -188,6 +188,7 @@ CONFIG_LCD_L4F00242T03=y
 CONFIG_LCD_PLATFORM=y
 CONFIG_BACKLIGHT_CLASS_DEVICE=y
 CONFIG_BACKLIGHT_PWM=y
+CONFIG_BACKLIGHT_GPIO=y
 CONFIG_FRAMEBUFFER_CONSOLE=y
 CONFIG_LOGO=y
 CONFIG_SOUND=y