powerpc: Enable device tree support for T2080RDB

Add device tree for T2080RDB board and enable CONFIG_OF_CONTROL
so that device tree can be compiled.
Update board README for device tree usage.

Signed-off-by: Hou Zhiqiang <Zhiqiang.Hou@nxp.com>
Reviewed-by: Prabhakar Kushwaha <prabhakar.kushwaha@nxp.com>
diff --git a/arch/powerpc/dts/t2080rdb.dts b/arch/powerpc/dts/t2080rdb.dts
new file mode 100644
index 0000000..49c1765
--- /dev/null
+++ b/arch/powerpc/dts/t2080rdb.dts
@@ -0,0 +1,17 @@
+// SPDX-License-Identifier: GPL-2.0+ OR X11
+/*
+ * T2080RDB Device Tree Source
+ *
+ * Copyright 2013 - 2015 Freescale Semiconductor Inc.
+ * Copyright 2019 NXP
+ */
+
+/include/ "t2080.dtsi"
+
+/ {
+	model = "fsl,T2080RDB";
+	compatible = "fsl,T2080RDB";
+	#address-cells = <2>;
+	#size-cells = <2>;
+	interrupt-parent = <&mpic>;
+};