dt-bindings: watchdog: Add i.MX7ULP bindings

Add the watchdog bindings for Freescale i.MX7ULP.
Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Reviewed-by: Rob Herring <rohb@kernel.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/1566999303-18795-1-git-send-email-Anson.Huang@nxp.comSigned-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

Documentation/devicetree/bindings/watchdog/fsl-imx7ulp-wdt.txt

+* Freescale i.MX7ULP Watchdog Timer (WDT) Controller
+
+Required properties:
+- compatible : Should be "fsl,imx7ulp-wdt"
+- reg : Should contain WDT registers location and length
+- interrupts : Should contain WDT interrupt
+- clocks: Should contain a phandle pointing to the gated peripheral clock.
+
+Optional properties:
+- timeout-sec : Contains the watchdog timeout in seconds
+
+Examples:
+
+wdog1: watchdog@403d0000 {
+	compatible = "fsl,imx7ulp-wdt";
+	reg = <0x403d0000 0x10000>;
+	interrupts = <GIC_SPI 55 IRQ_TYPE_LEVEL_HIGH>;
+	clocks = <&pcc2 IMX7ULP_CLK_WDG1>;
+	assigned-clocks = <&pcc2 IMX7ULP_CLK_WDG1>;
+	assigned-clocks-parents = <&scg1 IMX7ULP_CLK_FIRC_BUS_CLK>;
+	timeout-sec = <40>;
+};