PCI: xgene: Update PCI config space remap function

PCI configuration space should be mapped with a memory region type that
generates on the CPU host bus non-posted write transations. Update the
driver to use the devm_pci_remap_cfg* interface to make sure the correct
memory mappings for PCI configuration space are used.

Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: Tanmay Inamdar <tinamdar@apm.com>