microblaze: Add missing undefs for UBI and UBIFS

In the case of missing flash usage disaple (undef)
all the UBI support in the same way as for JFFS2.

Signed-off-by: Stephan Linz <linz@li-pro.net>
diff --git a/include/configs/microblaze-generic.h b/include/configs/microblaze-generic.h
index 1de6c69..e20eb08 100644
--- a/include/configs/microblaze-generic.h
+++ b/include/configs/microblaze-generic.h
@@ -306,6 +306,8 @@
 # undef CONFIG_CMD_IMLS
 # undef CONFIG_CMD_FLASH
 # undef CONFIG_CMD_JFFS2
+# undef CONFIG_CMD_UBI
+# undef CONFIG_CMD_UBIFS
 #endif
 
 #if defined(CONFIG_CMD_JFFS2)