PCI: dwc: Use parent_bus_offset to remove need for .cpu_addr_fixup()

PCI: dwc: Use parent_bus_offset to remove need for .cpu_addr_fixup()

We know the parent_bus_offset, either computed from a DT reg property (the
offset is the CPU physical addr - the 'config'/'addr_space' address on the
parent bus) or from a .cpu_addr_fixup() (which may have used a host bridge
window offset).

Apply that parent_bus_offset instead of calling .cpu_addr_fixup() when
programming the ATU.

This assumes all intermediate addresses are at the same offset from the CPU
physical addresses.

[bhelgaas: commit log]
Link: https://lore.kernel.org/r/20250315201548.858189-13-helgaas@kernel.org
Signed-off-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>