qga: Add initial FreeBSD support

- Fix device path.
- Fix virtio-serial channel initialization.
- Make the code buildable in FreeBSD.

Reviewed-by: Konstantin Kostiuk <kkostiuk@redhat.com>
Acked-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Alexander Ivanov <alexander.ivanov@virtuozzo.com>
Signed-off-by: Konstantin Kostiuk <kkostiuk@redhat.com>
4 files changed