util-lib: move a number of fs operations into fs-util.[ch]

src/nspawn/nspawn-mount.c

@@ -24,6 +24,7 @@
 
 #include "cgroup-util.h"
 #include "escape.h"
+#include "fs-util.h"
 #include "label.h"
 #include "mkdir.h"
 #include "mount-util.h"

src/nspawn/nspawn.c

@@ -61,6 +61,7 @@
 #include "fdset.h"
 #include "fileio.h"
 #include "formats-util.h"
+#include "fs-util.h"
 #include "gpt.h"
 #include "hostname-util.h"
 #include "log.h"