pinctrl: imx8mn: Support building as module

Change configuration to "tristate", add module device table,
author, description and license to support building i.MX8MN
pinctrl driver as module.

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Reviewed-by: Dong Aisheng <aisheng.dong@nxp.com>
Link: https://lore.kernel.org/r/1592979844-18833-5-git-send-email-Anson.Huang@nxp.com


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>