PCI: dwc: dra7xx: Populate cpu_addr_fixup ops

Populate cpu_addr_fixup ops to extract the least 28 bits of the
corresponding CPU address.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Joao Pinto <jpinto@synopsys.com>