PCI: intel-gw: Remove intel_pcie_cpu_addr()

Remove intel_pcie_cpu_addr(), the .cpu_addr_fixup() method, because the dwc
core driver already handles address translation based on the devicetree
description.

[bhelgaas: this does require a minor dts change, but maintainer
Lei Chuan Hua <lchuanhua@maxlinear.com> confirms that the driver is only
used internally to Maxlinear and internal users will update dts:
https://lore.kernel.org/r/BY3PR19MB507667CE7531D863E1E5F8AEBDD82@BY3PR19MB5076.namprd19.prod.outlook.com]

Link: https://lore.kernel.org/r/20250305-intel-v1-1-40db3a685490@nxp.com


Signed-off-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>