PCI: Init PCIe feature bits for managed host bridge alloc

Two functions allocate a host bridge: devm_pci_alloc_host_bridge() and
pci_alloc_host_bridge().  At the moment, only the unmanaged one initializes
the PCIe feature bits, which prevents from using features such as hotplug
or AER on some systems, when booting with device tree.  Make the
initialization code common.

Fixes: 02bfeb48 ("PCI/portdrv: Simplify PCIe feature permission checking")
Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
CC: stable@vger.kernel.org	# v4.17+