gc: Renamed lfsr_gc -> lfsr_fs_gc, keep lfsr_fs_unck in non-gc

- lfsr_gc -> lfsr_fs_gc
- lfsr_gc_unck -> lfsr_fs_unck

lfsr_fs_unck is surprisingly still useful in non-gc builds, since we
still have ckmeta/ckdata state. These flags can still be queried with
lfsr_fs_stat and cleared with lfsr_fs_ckmeta/ckdata/lfsr_traversal_t, so
it seems useful to keep this function around.

It's also a relatively cheap function.

Though this does mean it deserves a rename. Dropping the gc prefix
hopefully makes it clearer this function is not entirely gc-specific.

And since we no longer have lfsr_gc_setflags/setsteps, it makes sense to
rename lfsr_gc back to lfsr_fs_gc, to be consistent with the other
filesystem-wide utilities.

Code changes, apparently lfsr_fs_unck costs 12 bytes:

                   code          stack          ctx
  default before: 37792           2608          620
  default after:  37804 (+0.0%)   2608 (+0.0%)  620 (+0.0%)

  gc before:      37938           2608          768
  gc after:       37940 (+0.0%)   2608 (+0.0%)  768 (+0.0%)

lfs.h

@@ -1258,35 +1258,6 @@ int lfsr_traversal_read(lfs_t *lfs, lfsr_traversal_t *t,
 int lfsr_traversal_rewind(lfs_t *lfs, lfsr_traversal_t *t);
 
 
-/// Incremental gc operations ///
-
-#ifdef LFS_GC
-// Perform any janitorial work that may be pending.
-//
-// The exact janitorial work depends on the configured flags and steps.
-//
-// Calling this function is not required, but may allow the offloading of
-// expensive janitorial work to a less time-critical code path.
-//
-// Returns a negative error code on failure.
-int lfsr_gc(lfs_t *lfs);
-#endif
-
-#ifdef LFS_GC
-// Mark janitorial work as incomplete.
-//
-// Any info flags passed to lfsr_gc_unck will be reset internally,
-// forcing the work to be redone.
-//
-// This is most useful for triggering new ckmeta/ckdata scans with
-// LFS_I_CANCKMETA and LFS_I_CANCKDATA. Otherwise littlefs will perform
-// only one scan after mount.
-//
-// Returns a negative error code on failure.
-int lfsr_gc_unck(lfs_t *lfs, uint32_t flags);
-#endif
-
-
 /// Filesystem-level filesystem operations
 
 // Find on-disk info about the filesystem
@@ -1341,6 +1312,30 @@ int lfsr_fs_ckmeta(lfs_t *lfs);
 int lfsr_fs_ckdata(lfs_t *lfs);
 #endif
 
+#ifdef LFS_GC
+// Perform any janitorial work that may be pending
+//
+// The exact janitorial work depends on the configured flags and steps.
+//
+// Calling this function is not required, but may allow the offloading of
+// expensive janitorial work to a less time-critical code path.
+//
+// Returns a negative error code on failure.
+int lfsr_fs_gc(lfs_t *lfs);
+#endif
+
+// Mark janitorial work as incomplete
+//
+// Any info flags passed to lfsr_gc_unck will be reset internally,
+// forcing the work to be redone.
+//
+// This is most useful for triggering new ckmeta/ckdata scans with
+// LFS_I_CANCKMETA and LFS_I_CANCKDATA. Otherwise littlefs will perform
+// only one scan after mount.
+//
+// Returns a negative error code on failure.
+int lfsr_fs_unck(lfs_t *lfs, uint32_t flags);
+
 #ifndef LFS_READONLY
 // Change the number of blocks used by the filesystem
 //