imx6q.dtsi: add pinctrl_usdhc3_5 for sabrelite/nitrogen6x
imx6q-nitrogen6x.dts: add gpio-keys
imx6q-sabrelite.dts: add gpio-keys
Nitrogen6x/Sabrelite: add backlight_lcd
Nitrogen6x/Sabrelite: add mtd partitions
imx6q-nitroge6x/sabrelite.dts: remove invalid gpios for pcie