dt-bindings: pinctrl: add imx7ulp pinctrl binding doc

i.MX 7ULP has three IOMUXC instances: IOMUXC0 for M4 ports,
IOMUXC1 for A7 ports and IOMUXC DDR for DDR interface.

This patch adds the IOMUXC1 support for A7.

Cc: Mark Rutland <mark.rutland@arm.com>
Cc: devicetree@vger.kernel.org
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Shawn Guo <shawnguo@kernel.org>
Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Documentation/devicetree/bindings/pinctrl/fsl,imx7ulp-pinctrl.txt

+* Freescale i.MX7ULP IOMUX Controller
+
+i.MX 7ULP has three IOMUXC instances: IOMUXC0 for M4 ports, IOMUXC1 for A7
+ports and IOMUXC DDR for DDR interface.
+
+Note:
+This binding doc is only for the IOMUXC1 support in A7 Domain and it only
+supports generic pin config.
+
+Please also refer pinctrl-bindings.txt in this directory for generic pinctrl
+binding.
+
+=== Pin Controller Node ===
+
+Required properties:
+- compatible:	"fsl,imx7ulp-iomuxc1"
+- reg:		Should contain the base physical address and size of the iomuxc
+		registers.
+
+=== Pin Configuration Node ===
+- pinmux: One integers array, represents a group of pins mux setting.
+	The format is pinmux = <PIN_FUNC_ID>, PIN_FUNC_ID is a pin working on
+	a specific function.
+
+	NOTE: i.MX7ULP PIN_FUNC_ID consists of 4 integers as it shares one mux
+	and config register as follows:
+	<mux_conf_reg input_reg mux_mode input_val>
+
+	Refer to imx7ulp-pinfunc.h in in device tree source folder for all
+	available imx7ulp PIN_FUNC_ID.
+
+Optional Properties:
+- drive-strength		Integer. Controls Drive Strength
+					0: Standard
+					1: Hi Driver
+- drive-push-pull		Bool. Enable Pin Push-pull
+- drive-open-drain		Bool. Enable Pin Open-drian
+- slew-rate:			Integer. Controls Slew Rate
+					0: Standard
+					1: Slow
+- bias-disable:			Bool. Pull disabled
+- bias-pull-down:		Bool. Pull down on pin
+- bias-pull-up:			Bool. Pull up on pin
+
+Examples:
+#include "imx7ulp-pinfunc.h"
+
+/* Pin Controller Node */
+iomuxc1: iomuxc@40ac0000 {
+	compatible = "fsl,imx7ulp-iomuxc1";
+	reg = <0x40ac0000 0x1000>;
+
+	/* Pin Configuration Node */
+	pinctrl_lpuart4: lpuart4grp {
+		pinmux = <
+			IMX7ULP_PAD_PTC3__LPUART4_RX
+			IMX7ULP_PAD_PTC2__LPUART4_TX
+		>;
+		bias-pull-up;
+	};
+};