arm: mvebu: Add CRS328-4C-20S-4S board

MikroTik CRS328-4C-20S-4S board has a switch chip with an integrated
Marvell Prestera 98DX3236 CPU.

This commit includes two board variants, namely the factory
default one and a Bit variant. The Bit board variant has a
bigger Macronix flash.

Add basic U-Boot, UART and SPI flash support.

Signed-off-by: Luka Kovacic <luka.kovacic@sartura.hr>
Cc: Luka Perkov <luka.perkov@sartura.hr>
Cc: Jakov Petrina <jakov.petrina@sartura.hr>
Reviewed-by: Stefan Roese <sr@denx.de>
diff --git a/arch/arm/dts/armada-xp-crs328-4c-20s-4s.dts b/arch/arm/dts/armada-xp-crs328-4c-20s-4s.dts
new file mode 100644
index 0000000..665757f
--- /dev/null
+++ b/arch/arm/dts/armada-xp-crs328-4c-20s-4s.dts
@@ -0,0 +1,17 @@
+// SPDX-License-Identifier: (GPL-2.0+ OR MIT)
+/*
+ * Device Tree file for MikroTik CRS328-4C-20S-4S+ board
+ *
+ * Copyright (C) 2020 Sartura Ltd.
+ * Author: Luka Kovacic <luka.kovacic@sartura.hr>
+ */
+
+#include "armada-xp-crs328-4c-20s-4s.dtsi"
+
+/ {
+	model = "MikroTik CRS328-4C-20S-4S+";
+};
+
+&spi0 {
+	status = "okay";
+};