RDMA/hns: Replace wmb&__raw_writeq with writeq

RDMA/hns: Replace wmb&__raw_writeq with writeq

Currently, the driver updates doorbell looks like this:

post()
{
	wqe.field = 0x111;
	wmb();
	update_wq_db();
}

update_wq_db()
{
	db.field = 0x222;
	__raw_writeq(db, db_reg);
}

writeq() is a better choice than __raw_writeq() because it calls dma_wmb()
to barrier in ARM64, and dma_wmb() is better than wmb() for ROCEE device.

This patch removes all wmb() before updating doorbell of SQ/RQ/CQ/SRQ by
replacing __raw_writeq() with writeq() to improve performence.  The new
process looks like this:

post()
{
	wqe.field = 0x111;
	update_wq_db();
}

update_wq_db()
{
	db.field = 0x222;
	writeq(db, db_reg);
}

Link: https://lore.kernel.org/r/1612517974-31867-8-git-send-email-liweihang@huawei.com
Signed-off-by: Lang Cheng <chenglang@huawei.com>
Signed-off-by: Weihang Li <liweihang@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>