vl.c: Abort on unknown -numa option type

Abort in case an invalid -numa option is provided, instead of silently
ignoring it.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
