PCI: dwc: Add dw_pcie_parent_bus_offset() checking and debug

dw_pcie_parent_bus_offset() looks up the parent bus address of a PCI
controller 'reg' property in devicetree.  If implemented, .cpu_addr_fixup()
is a hard-coded way to get the parent bus address corresponding to a CPU
physical address.

Add debug code to compare the address from .cpu_addr_fixup() with the
address from devicetree.  If they match, warn that .cpu_addr_fixup() is
redundant and should be removed; if they differ, warn that something is
wrong with the devicetree.

If .cpu_addr_fixup() is not implemented, the parent bus address should be
identical to the CPU physical address because we previously ignored the
parent bus address from devicetree.  If the devicetree has a different
parent bus address, warn about it being broken.

[bhelgaas: split debug to separate patch for easier future revert, commit
log]

Link: https://lore.kernel.org/r/20250315201548.858189-7-helgaas@kernel.org


Signed-off-by: Frank Li <Frank.Li@nxp.com>
[bhelgaas: squash Ioana Ciornei <ioana.ciornei@nxp.com> fix for NULL
pointer deref when driver doesn't supply dw_pcie_ops, e.g., layerscape-pcie
https://lore.kernel.org/r/20250319134339.3114817-1-ioana.ciornei@nxp.com

]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>