arm: switch armltd vexpress to GENERIC_BOARD

only tested tested under QEMU with vexpress_ca9x4 ("-M vexpress-a9") and
vexpress_ca15_tc2 ("-M vexpress-a15"). Makes the ugly warning go away.

Signed-off-by: Chris Kuethe <chris.kuethe+github@gmail.com>
diff --git a/include/configs/vexpress_common.h b/include/configs/vexpress_common.h
index 7e78f8a..2dea921 100644
--- a/include/configs/vexpress_common.h
+++ b/include/configs/vexpress_common.h
@@ -122,7 +122,7 @@
 #define CONFIG_SETUP_MEMORY_TAGS	1
 #define CONFIG_SYS_L2CACHE_OFF		1
 #define CONFIG_INITRD_TAG		1
-
+#define CONFIG_SYS_GENERIC_BOARD
 #define CONFIG_OF_LIBFDT		1
 
 /* Size of malloc() pool */