PCI: Don't auto-realloc if we're preserving firmware config

Prevent auto-enabling of bridges reallocation when the FW tells us that the
initial configuration must be preserved for a given host bridge.

Link: https://lore.kernel.org/r/20190615002359.29577-3-benh@kernel.crashing.org


Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>