This check isn't exclusive to XML parsing. Let's move it to
virDomainDefVideoValidate() in domain_validate.c
We don't have a failure test for this scenario, so a new test called
'video-multiple-primaries' was added to test this failure case.
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
