iommu: arm-smmu: Handoff SMR registers and context banks

Boot splash screen or EFI framebuffer requires the display hardware to
operate while the Linux iommu driver probes. Therefore, we cannot simply
wipe out the SMR register settings programmed by the bootloader.

Detect which SMR registers are in use during probe, and which context
banks they are associated with. Reserve these context banks for the
first Linux device whose stream-id matches the SMR register.

Any existing page-tables will be discarded.

Heavily based on downstream implementation by Patrick Daly
<pdaly@codeaurora.org>.

Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Ondrej Kubik <ondrej.kubik@canonical.com>