[LogFS] add new flash file system

This is a new flash file system. See
Documentation/filesystems/logfs.txt

Signed-off-by: Joern Engel <joern@logfs.org>
diff --git a/lib/Kconfig b/lib/Kconfig
index bb1326d..277fbfb 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -156,6 +156,9 @@
 config TEXTSEARCH_FSM
 	tristate
 
+config BTREE
+	boolean
+
 config HAS_IOMEM
 	boolean
 	depends on !NO_IOMEM