domain_conf: Remove zPCI validation from formatter

domain_conf: Remove zPCI validation from formatter

In 076591009ad a validation code was added to
virDomainDeviceInfoFormat() which reports an error if zPCI
address entered in was incomplete. But, there are two problems
with this approach.

The first problem is the placement of the code - it doesn't
belong into XML formatter rather than XML validator.

The second one is that at the point of formatting XML the post
parse callback has run and thus filled in required info.
Therefore this check can never do something useful and instead of
moving it into validator, it's removed completely.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Andrea Bolognani <abologna@redhat.com>