pinctrl: imx: add VF610 support to imx pinctrl framework

On some platforms such as VF610, offset of mux and pad ctrl register
may be zero, and the mux_mode and config_val are in one 32-bit register.
This patch adds support to imx core pinctrl framework to handle these
cases.

Signed-off-by: Jingchang Lu <b35083@freescale.com>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>