dt-bindings: mips: Add bindings for Microsemi SoCs

Add bindings for Microsemi SoCs. Currently only Ocelot is supported.
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Reviewed-by: Rob Herring <robh+dt@kernel.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Allan Nielsen <Allan.Nielsen@microsemi.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/18854/Signed-off-by: James Hogan <jhogan@kernel.org>

Documentation/devicetree/bindings/mips/mscc.txt

+* Microsemi MIPS CPUs
+
+Boards with a SoC of the Microsemi MIPS family shall have the following
+properties:
+
+Required properties:
+- compatible: "mscc,ocelot"
+
+
+* Other peripherals:
+
+o CPU chip regs:
+
+The SoC has a few registers (DEVCPU_GCB:CHIP_REGS) handling miscellaneous
+functionalities: chip ID, general purpose register for software use, reset
+controller, hardware status and configuration, efuses.
+
+Required properties:
+- compatible: Should be "mscc,ocelot-chip-regs", "simple-mfd", "syscon"
+- reg : Should contain registers location and length
+
+Example:
+	syscon@71070000 {
+		compatible = "mscc,ocelot-chip-regs", "simple-mfd", "syscon";
+		reg = <0x71070000 0x1c>;
+	};
+
+
+o CPU system control:
+
+The SoC has a few registers (ICPU_CFG:CPU_SYSTEM_CTRL) handling configuration of
+the CPU: 8 general purpose registers, reset control, CPU en/disabling, CPU
+endianness, CPU bus control, CPU status.
+
+Required properties:
+- compatible: Should be "mscc,ocelot-cpu-syscon", "syscon"
+- reg : Should contain registers location and length
+
+Example:
+	syscon@70000000 {
+		compatible = "mscc,ocelot-cpu-syscon", "syscon";
+		reg = <0x70000000 0x2c>;
+	};