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

The continuous splash screen feature 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 this context bank for the first linux
device whose stream-id matches the SMR register.

Only context banks which have SCTLR.M bit set to 0 are allowed; any
existing page-tables will be discarded.

Change-Id: Iecce61b38b36db01db4fd2d26b6d4451e68c04da
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>