pinctrl: freescale: Add imx8mm pinctrl driver support

Add the pinctrl driver support for i.MX8MM.

Signed-off-by: Bai Ping <ping.bai@nxp.com>
Acked-by: Aisheng Dong <aisheng.dong@nxp.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>