pinctrl: imx: Support i.MX8 SoCs pinctrl driver built as module

Export necessary APIs to support i.MX8 SoCs pinctrl driver to be
built 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/1592979844-18833-2-git-send-email-Anson.Huang@nxp.com


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