ARM: dts: Add OpenBMC flash layout

This is a layout used by OpenBMC systems. It describes the fixed flash
layout of a 32MB mtd device.
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Joel Stanley <joel@jms.id.au>

arch/arm/boot/dts/openbmc-flash-layout.dtsi

+// SPDX-License-Identifier: GPL-2.0+
+
+partitions {
+	compatible = "fixed-partitions";
+	#address-cells = <1>;
+	#size-cells = <1>;
+
+	u-boot@0 {
+		reg = <0x0 0x60000>;
+		label = "u-boot";
+	};
+
+	u-boot-env@60000 {
+		reg = <0x60000 0x20000>;
+		label = "u-boot-env";
+	};
+
+	kernel@80000 {
+		reg = <0x80000 0x440000>;
+		label = "kernel";
+	};
+
+	rofs@c0000 {
+		reg = <0x4c0000 0x1740000>;
+		label = "rofs";
+	};
+
+	rwfs@1c00000 {
+		reg = <0x1c00000 0x400000>;
+		label = "rwfs";
+	};
+};