pinctrl: imx7d: simplify imx7d_pinctrl_probe

Using of_device_get_match_data in imx7d_pinctrl_probe simplifies
the function. Also get rid of the void pointer cast since
imx_pinctrl_probe now accepts const struct imx_pinctrl_soc_info.

Cc: Arvind Yadav <arvind.yadav.cs@gmail.com>
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>