pinctrl: imx: add gpio pinmux support for vf610

Add pinmux support for GPIO for Vybrid (vf610) IOMUX controller.
This is needed since direction configuration is not part of the
GPIO module in Vybrid.

Signed-off-by: Stefan Agner <stefan@agner.ch>
Acked-by: Shawn Guo <shawn.guo@freescale.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>