PCI: hv: Set ->domain_nr of pci_host_bridge at probing time

PCI: hv: Set ->domain_nr of pci_host_bridge at probing time

No functional change, just store and maintain the PCI domain number in
the ->domain_nr of pci_host_bridge. Note that we still need to keep
the copy of domain number in x86-specific pci_sysdata, because x86 is
not a PCI_DOMAINS_GENERIC=y architecture, so the ->domain_nr of
pci_host_bridge doesn't work for it yet.

Link: https://lore.kernel.org/r/20210726180657.142727-7-boqun.feng@gmail.com
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>