vl: Add another sanity check to smp_parse() function

The code in smp_parse already checks the topology information for
sockets * cores * threads < cpus and bails out with an error in
that case. However, it is still possible to supply a bad configuration
the other way round, e.g. with:

 qemu-system-xxx -smp 4,sockets=1,cores=4,threads=2

QEMU then still starts the guest, with topology configuration that
is rather incomprehensible and likely not what the user wanted.
So let's add another check to refuse such wrong configurations.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Acked-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Acked-by: Bastian Koppelmann <kbastian@mail.uni-paderborn.de>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
