fs/iso9660: enable Joliet extension

We already enable the Rockridge extension by default when building
ISO9660, so let's also enable the Joliet extension which allows to
support Unicode file names and long file names.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: Samuel Martin <s.martin49@gmail.com>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>