PCI: dwc: Rename cpu_addr to parent_bus_addr for ATU configuration

PCI: dwc: Rename cpu_addr to parent_bus_addr for ATU configuration

Rename 'cpu_addr' to 'parent_bus_addr' in the DesignWare ATU configuration.

The ATU translates parent bus addresses to PCI addresses, which are often
the same as CPU addresses but can differ in systems where the bus fabric
translates addresses before passing them to the PCIe controller. This
renaming clarifies the purpose and avoids confusion.

Link: https://lore.kernel.org/r/20250315201548.858189-3-helgaas@kernel.org
Signed-off-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>