util-lib: move some functions from basic/cgroup-util to shared/cgroup-setup

This way less stuff needs to be in basic. Initially, I wanted to move all the
parts of cgroup-utils.[ch] that depend on efivars.[ch] to shared, because
efivars.[ch] is in shared/. Later on, I decide to split efivars.[ch], so the
move done in this patch is not necessary anymore. Nevertheless, it is still
valid on its own. If at some point we want to expose libbasic, it is better to
to not have stuff that belong in libshared there.

src/nspawn/nspawn-cgroup.c

@@ -3,6 +3,7 @@
 #include <sys/mount.h>
 
 #include "alloc-util.h"
+#include "cgroup-setup.h"
 #include "fd-util.h"
 #include "fileio.h"
 #include "format-util.h"