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: Joshua Henderson <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Cc: Pawel Moll <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: Ian Campbell <[e-mail]>
Cc: Kumar Gala <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Patchwork: https://patchwork.linux-mips.org/patch/12096/
Signed-off-by: Ralf Baechle <[e-mail]>

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.