ARM: dts: mxs: add hog-gpios for imx23-evk and imx28-evk

Before gpio_request can directly ask pinctrl system to configure the
requested pin into gpio mode, we use "hog" entry (pinctrl state of
pin controller itself) to configure gpios.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>