fs: Move file system code to subsys/

Subsystems code will reside in subsys/ folder. This patch creates the
folder and moves FS code there.

Jira: ZEP-1120
Change-Id: If3b1bcb996c5fbd4056cd5d1920d41d29810d6b2
Signed-off-by: Ramesh Thomas <ramesh.thomas@intel.com>
diff --git a/Kconfig.zephyr b/Kconfig.zephyr
index 6d513a6..2f33a2a 100644
--- a/Kconfig.zephyr
+++ b/Kconfig.zephyr
@@ -32,7 +32,7 @@
 
 source "lib/Kconfig"
 
-source "fs/Kconfig"
+source "subsys/Kconfig"
 
 source "ext/Kconfig"