fs: ext4: implement opendir, readdir, closedir

For accessing directories from the EFI sub-system a file system must
implement opendir, readdir, closedir. Provide the missing implementation.

With this patch the eficonfig command can be used to define load options
for the ext4 file system.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/fs/fs.c b/fs/fs.c
index e2915e7..a515905 100644
--- a/fs/fs.c
+++ b/fs/fs.c
@@ -232,7 +232,9 @@
 		.ln = fs_ln_unsupported,
 #endif
 		.uuid = ext4fs_uuid,
-		.opendir = fs_opendir_unsupported,
+		.opendir = ext4fs_opendir,
+		.readdir = ext4fs_readdir,
+		.closedir = ext4fs_closedir,
 		.unlink = fs_unlink_unsupported,
 		.mkdir = fs_mkdir_unsupported,
 	},