pinctrl: imx: constify struct imx_pinctrl_soc_info

Now that imx_pinctrl_probe accepts const struct imx_pinctrl_soc_info
we can constify all declarations of struct imx_pinctrl_soc_info.

Signed-off-by: Stefan Agner <stefan@agner.ch>
Acked-by: Dong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>