freevxfs: Convert freevxfs to the new mount API.

Convert the freevxfs filesystem to the new mount API.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Link: https://lore.kernel.org/r/b0d1a423-4b8e-4bc1-a021-a1078aee915f@redhat.com


Tested-by: Krzysztof Błaszkowski <kb@sysmikro.com.pl>
Signed-off-by: Christian Brauner <brauner@kernel.org>