MSCC: add board support for the Luton based evaluation board

Adding the support for the Luton boards PCB91 which share common code with
the Ocelots boards, including board code, device tree and configuration.

Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>

arch/mips/dts/luton_pcb091.dts

@@ -0,0 +1,36 @@
+// SPDX-License-Identifier: (GPL-2.0+ OR MIT)
+/*
+ * Copyright (c) 2018 Microsemi Corporation
+ */
+
+/dts-v1/;
+#include "mscc,luton.dtsi"
+
+/ {
+	model = "Luton10 PCB091 Reference Board";
+	compatible = "mscc,luton-pcb091", "mscc,luton";
+
+	aliases {
+		serial0 = &uart0;
+		spi0 = &spi0;
+	};
+
+	chosen {
+		stdout-path = "serial0:115200n8";
+	};
+};
+
+&uart0 {
+	status = "okay";
+};
+
+&spi0 {
+	status = "okay";
+	spi-flash@0 {
+		compatible = "spi-flash";
+		spi-max-frequency = <18000000>; /* input clock */
+		reg = <0>; /* CS0 */
+		spi-cs-high;
+	};
+};
+