Added lfs_fs_stat for accessing configuration in the superblocks

This is necessary for accessing format-specific information stored in
the superblock after mounting.

As is common in other filesystems this also provides the filesystem
usage. However collecting the filesystem usage is more expensive in
littlefs than other filesystem (and less accurate because of CoW), so
this may need to be cached after mount in the future.

lfs.c

@@ -4825,6 +4825,21 @@ static lfs_ssize_t lfs_fs_rawsize(lfs_t *lfs) {
     return size;
 }
 
+static int lfs_fs_rawstat(lfs_t *lfs, struct lfs_fsinfo *fsinfo) {
+    lfs_ssize_t usage = lfs_fs_rawsize(lfs);
+    if (usage < 0) {
+        return usage;
+    }
+
+    fsinfo->block_size = lfs->block_size;
+    fsinfo->block_count = lfs->block_count;
+    fsinfo->block_usage = usage;
+    fsinfo->name_max = lfs->name_max;
+    fsinfo->file_max = lfs->file_max;
+    fsinfo->attr_max = lfs->attr_max;
+    return 0;
+}
+
 #ifdef LFS_MIGRATE
 ////// Migration from littelfs v1 below this //////
 
@@ -5948,6 +5963,20 @@ int lfs_dir_rewind(lfs_t *lfs, lfs_dir_t *dir) {
     return err;
 }
 
+int lfs_fs_stat(lfs_t *lfs, struct lfs_fsinfo *fsinfo) {
+    int err = LFS_LOCK(lfs->cfg);
+    if (err) {
+        return err;
+    }
+    LFS_TRACE("lfs_fs_stat(%p, %p)", (void*)lfs, (void*)fsinfo);
+
+    err = lfs_fs_rawstat(lfs, fsinfo);
+
+    LFS_TRACE("lfs_fs_stat -> %d", err);
+    LFS_UNLOCK(lfs->cfg);
+    return err;
+}
+
 lfs_ssize_t lfs_fs_size(lfs_t *lfs) {
     int err = LFS_LOCK(lfs->cfg);
     if (err) {