ib: Eliminate duplicate barriers on weakly-ordered archs

Code includes wmb() followed by writel() in multiple places. writel() already has a barrier on some architectures like arm64.

This ends up CPU observing two barriers back to back before executing the register write.

Since code already has an explicit barrier call, changing writel() to writel_relaxed().

I did a regex search for wmb() followed by writel() in each drivers directory.
I scrubbed the ones I care about in this series.

I considered "ease of change", "popular usage" and "performance critical path" as the determining criteria for my filtering.

We used relaxed API heavily on ARM for a long time but
it did not exist on other architectures. For this reason, relaxed architectures have been paying double penalty in order to use the common drivers.

Now that relaxed API is present on all architectures, we can go and scrub all drivers to see what needs to change and what can remain.

We start with mostly used ones and hope to increase the coverage over time. It will take a while to cover all drivers.

Feel free to apply patches individually.

Changes since v3:
- https://www.spinics.net/lists/arm-kernel/msg641851.html
- group patches together into subsystems ib:...
- collect reviewed and tested bys
- scrub barrier()

Sinan Kaya (6):
IB/mlx4: Eliminate duplicate barriers on weakly-ordered archs
infiniband: cxgb4: Eliminate duplicate barriers on weakly-ordered
archs

RDMA/bnxt_re: Eliminate duplicate barriers on weakly-ordered archs RDMA/i40iw: Eliminate duplicate barriers on weakly-ordered archs IB/nes: Eliminate duplicate barriers on weakly-ordered archs RDMA/qedr: eliminate duplicate barriers on weakly-ordered archs #2