pinctrl: imx: add imx8qxp driver

MX8QXP contains a system controller that is responsible for controlling
the pad setting of the IPs that are present. Communication between the
host processor running an OS and the system controller happens through
a SCU protocol. This patch adds the SCU based MX8QXP pinctrl driver.

Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Shawn Guo <shawnguo@kernel.org>
Cc: Fabio Estevam <festevam@gmail.com>
Cc: Stefan Agner <stefan@agner.ch>
Cc: Pengutronix Kernel Team <kernel@pengutronix.de>
Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>