dt/bindings: Add bindings for PIC32 watchdog peripheral

Document the devicetree bindings for the watchdog peripheral found on
Microchip PIC32 SoC class devices.
Signed-off-by: Joshua Henderson <joshua.henderson@microchip.com>
Acked-by: Rob Herring <robh@kernel.org>
Cc: Pawel Moll <pawel.moll@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Ian Campbell <ijc+devicetree@hellion.org.uk>
Cc: Kumar Gala <galak@codeaurora.org>
Cc: Wim Van Sebroeck <wim@iguana.be>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: linux-kernel@vger.kernel.org
Cc: linux-mips@linux-mips.org
Cc: devicetree@vger.kernel.org
Cc: linux-watchdog@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/12700/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

Documentation/devicetree/bindings/watchdog/microchip,pic32-wdt.txt

+* Microchip PIC32 Watchdog Timer
+
+When enabled, the watchdog peripheral can be used to reset the device if the
+WDT is not cleared periodically in software.
+
+Required properties:
+- compatible: must be "microchip,pic32mzda-wdt".
+- reg: physical base address of the controller and length of memory mapped
+  region.
+- clocks: phandle of source clk. should be <&LPRC> clk.
+
+Example:
+
+	watchdog@1f800800 {
+		compatible = "microchip,pic32mzda-wdt";
+		reg = <0x1f800800 0x200>;
+		clocks = <&LPRC>;
+	};