iommu/arm-smmu: Pass io-pgtable config to implementation specific function

Construct the io-pgtable config before calling the implementation specific
init_context function and pass it so the implementation specific function
can get a chance to change it before the io-pgtable is created.

Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Will Deacon <will@kernel.org>