PCI: xgene: Allow config access to Root Port even when link is down

Previously, when a Root Port's link was down, we didn't allow config access
to the Root Port, which meant that if the Root Port led to an empty slot,
"lspci" didn't even show the Root Port.

Allow config access to Root Port even when link is down.

[bhelgaas: changelog, fold in unused var fix]
Suggested-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Duc Dang <dhdang@apm.com>
Signed-off-by: Tanmay Inamdar <tinamdar@apm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>