PCI: dwc: Allow drivers to skip MEM outbound iATU setup

Some DWC-based controllers do not require outbound iATU windows for MEM
transactions. For those platforms, programming outbound iATU windows for
host bridge MEM ranges is unnecessary and may constrain the available MEM
aperture.

The DWC PCIe RP Controller Databook v6.00a, section 3.12.2, describes the
default outbound no-match behavior as pass-through. Section 3.12.5.6, "No
Address Match Result", says the address is not translated and programmable
TLP header fields come from the application transmit interface.

This no-match path cannot translate between different parent-bus and PCI
addresses, so require skipped MEM ranges to be identity-mapped.

Add dw_pcie_rp->bypass_ob_mem_iatu so drivers can skip generic MEM iATU
setup while using the common DWC host init path.

Existing drivers keep the current behavior because the flag defaults to
false. The I/O iATU setup does not use the MEM resource iterator, and the
iterator may be uninitialized when MEM setup is skipped. Avoid using it in
the I/O iATU error path.

Signed-off-by: Xincheng Zhang <zhangxincheng@ultrarisc.com>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@oss.qualcomm.com>
Link: https://patch.msgid.link/20260905025635.211390-2-zhangxincheng@ultrarisc.com

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