UBIFS: include to compilation

Add UBIFS to Makefile and Kbuild.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: Adrian Hunter <ext-adrian.hunter@nokia.com>
diff --git a/fs/Kconfig b/fs/Kconfig
index 2694648..a52cf62 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -1375,6 +1375,9 @@
 
 endchoice
 
+# UBIFS File system configuration
+source "fs/ubifs/Kconfig"
+
 config CRAMFS
 	tristate "Compressed ROM file system support (cramfs)"
 	depends on BLOCK