Move vl.c to a separate directory, similar to linux-user/
Update the chechpatch and get_maintainer scripts, since they relied on
/vl.c for top_of_tree checks.

Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Message-id: 20200220041118.23264-2-alxndr@bu.edu
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>