fsdev: Move some types definition to qemu-fsdev.c

fsdev: Move some types definition to qemu-fsdev.c

It would make sense for these types to be defined in a header file if
we had an API for fsdrivers to register themselves. In practice, we
only have three of them and it is very unlikely we add new ones since
the future of file sharing between host and guest is the upcoming
virtio-fs.

Move the types to qemu-fsdev.c instead since they are only used there.

Signed-off-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>