iommu/arm-smmu: Setup identity domain for boot mappings

With many Qualcomm platforms not having functional S2CR BYPASS a
temporary IOMMU domain, without translation, needs to be allocated in
order to allow these memory transactions.

Unfortunately the boot loader uses the first few context banks, so
rather than overwriting a active bank the last context bank is used and
streams are diverted here during initialization.

This also performs the readback of SMR registers for the Qualcomm
platform, to trigger the mechanism.

This is based on prior work by Thierry Reding and Laurentiu Tudor.

Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Message-Id: <20200709050145.3520931-6-bjorn.andersson@linaro.org>
Signed-off-by: Vinod Koul <vkoul@kernel.org>