x86/PCI: reduce severity of host bridge window conflict warnings

Host bridge windows are top-level resources, so if we find a host bridge
window conflict, it's probably with a hard-coded legacy reservation.
Moving host bridge windows is theoretically possible, but we don't support
it; we just ignore windows with conflicts, and it's not worth making this
a user-visible error.

Reported-and-tested-by: Jools Wills <jools@oxfordinspire.co.uk>
References: https://bugzilla.kernel.org/show_bug.cgi?id=38522


Reported-by: Das <dasfox@gmail.com>
References: https://bugzilla.kernel.org/show_bug.cgi?id=16497


Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>