dt/bindings: Add bindings for PIC32/MZDA platforms

This adds support for the Microchip PIC32 platform along with the
specific variant PIC32MZDA on a PIC32MZDA Starter Kit.
Signed-off-by: NJoshua Henderson <joshua.henderson@microchip.com>
Acked-by: NRob 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: linux-kernel@vger.kernel.org
Cc: linux-mips@linux-mips.org
Cc: devicetree@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/12096/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

Documentation/devicetree/bindings/mips/pic32/microchip,pic32mzda.txt

+* Microchip PIC32MZDA Platforms
+
+PIC32MZDA Starter Kit
+Required root node properties:
+    - compatible = "microchip,pic32mzda-sk", "microchip,pic32mzda"
+
+CPU nodes:
+----------
+A "cpus" node is required.  Required properties:
+ - #address-cells: Must be 1.
+ - #size-cells: Must be 0.
+A CPU sub-node is also required.  Required properties:
+ - device_type: Must be "cpu".
+ - compatible: Must be "mti,mips14KEc".
+Example:
+	cpus {
+		#address-cells = <1>;
+		#size-cells = <0>;
+
+		cpu0: cpu@0 {
+			device_type = "cpu";
+			compatible = "mti,mips14KEc";
+		};
+	};
+
+Boot protocol
+--------------
+In accordance with Unified Hosting Interface Reference Manual (MD01069), the
+bootloader must pass the following arguments to the kernel:
+ - $a0: -2.
+ - $a1: KSEG0 address of the flattened device-tree blob.