cmd: fs: Add command to list supported fs types

Added command "fstypes" to list supported/included filesystems.

Signed-off-by: Niel Fourie <lusus@denx.de>
Cc: Simon Glass <sjg@chromium.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
[trini: Limit to sandbox]
Signed-off-by: Tom Rini <trini@konsulko.com>

test/py/tests/test_fs/test_fs_cmd.py

@@ -0,0 +1,13 @@
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (C) 2020
+# Niel Fourie, DENX Software Engineering, lusus@denx.de
+
+import pytest
+
+@pytest.mark.boardspec('sandbox')
+@pytest.mark.buildconfigspec('cmd_fs_generic')
+def test_dm_compat(u_boot_console):
+    """Test that `fstypes` prints a result which includes `sandbox`."""
+    output = u_boot_console.run_command('fstypes')
+    assert "Supported filesystems:" in output
+    assert "sandbox" in output