MIPS: kconfig: add options for dbau1x00 board variant select

The dbau1x00 board can be built with various variants which are
configured via CONFIG_SYS_EXTRA_OPTIONS. This is deprecated. Thus
add new Kconfig options for those board variants.

Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
diff --git a/board/dbau1x00/Kconfig b/board/dbau1x00/Kconfig
index 3e3cb77..1286e45 100644
--- a/board/dbau1x00/Kconfig
+++ b/board/dbau1x00/Kconfig
@@ -9,4 +9,22 @@
 config SYS_CONFIG_NAME
 	default "dbau1x00"
 
+menu "dbau1x00 board options"
+
+choice
+	prompt "Select au1x00 SoC type"
+
+config DBAU1100
+	bool "Select AU1100"
+
+config DBAU1500
+	bool "Select AU1500"
+
+config DBAU1550
+	bool "Select AU1550"
+
+endchoice
+
+endmenu
+
 endif