DT: MIPS: ralink: add RT2880 dts files

Add a dtsi file for RT2880 SoC and a sample dts file.

Signed-off-by: John Crispin <blogic@openwrt.org>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Patchwork: http://patchwork.linux-mips.org/patch/5188/
diff --git a/arch/mips/ralink/Kconfig b/arch/mips/ralink/Kconfig
index 86f6c77..2f6fbb8 100644
--- a/arch/mips/ralink/Kconfig
+++ b/arch/mips/ralink/Kconfig
@@ -34,6 +34,10 @@
 	config DTB_RT_NONE
 		bool "None"
 
+	config DTB_RT2880_EVAL
+		bool "RT2880 eval kit"
+		depends on SOC_RT288X
+
 	config DTB_RT305X_EVAL
 		bool "RT305x eval kit"
 		depends on SOC_RT305X