pinctrl: fsl: add scu based pinctrl support

Some i.MX SoCs (e.g. MX8QXP and MX8QM) contain 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 classifies the pad settings into two categories: MMIO and SCU.
For the original MMIO method, no functional changes except organize them
into a few imx_*_mmio() functions. Besides that, we add the SCU based
Pad Mux and Pinconf setting support which are implemented in pinctrl-scu.c.

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>
diff --git a/drivers/pinctrl/freescale/Makefile b/drivers/pinctrl/freescale/Makefile
index 73175b3..7ac8daf 100644
--- a/drivers/pinctrl/freescale/Makefile
+++ b/drivers/pinctrl/freescale/Makefile
@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0
 # Freescale pin control drivers
 obj-$(CONFIG_PINCTRL_IMX)	+= pinctrl-imx.o
+obj-$(CONFIG_PINCTRL_IMX_SCU)	+= pinctrl-scu.o
 obj-$(CONFIG_PINCTRL_IMX1_CORE)	+= pinctrl-imx1-core.o
 obj-$(CONFIG_PINCTRL_IMX1)	+= pinctrl-imx1.o
 obj-$(CONFIG_PINCTRL_IMX21)	+= pinctrl-imx21.o