Add Btrfs to fs/Kconfig and fs/Makefile

Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/Makefile b/fs/Makefile
index a1482a5..41fcc85 100644
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -121,4 +121,5 @@
 obj-$(CONFIG_HPPFS)		+= hppfs/
 obj-$(CONFIG_DEBUG_FS)		+= debugfs/
 obj-$(CONFIG_OCFS2_FS)		+= ocfs2/
+obj-$(CONFIG_BTRFS_FS)		+= btrfs/
 obj-$(CONFIG_GFS2_FS)           += gfs2/