pinctrl: imx: Support building SCU pinctrl core driver as module

Change PINCTR_IMX_SCU to tristate, add module author, description
and license to support building SCU pinctrl core 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/1599552721-24872-2-git-send-email-Anson.Huang@nxp.com


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