iommu/arm-smmu: Add a way for implementations to influence SCTLR

iommu/arm-smmu: Add a way for implementations to influence SCTLR

For the Adreno GPU's SMMU, we want SCTLR.HUPCF set to ensure that
pending translations are not terminated on iova fault.  Otherwise
a terminated CP read could hang the GPU by returning invalid
command-stream data. Add a hook to for the implementation to modify
the sctlr value if it wishes.

Co-developed-by: Jordan Crouse <jcrouse@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>
Link: https://lore.kernel.org/r/20201109184728.2463097-3-jcrouse@codeaurora.org
Signed-off-by: Will Deacon <will@kernel.org>