iommu/arm-smmu: Add configuration implementation hook

Probing the ID registers and setting up the SMMU configuration is an
area where overrides and workarounds may well be needed. Indeed, the
Cavium workaround detection lives there at the moment, so let's break
that out.

Change-Id: I2b828a98981866a1a5adf21555055b8a4c9788d2
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
Git-commit: 3995e186
Git-repo: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


[isaacm@codeauora.org: resolve trivial merge conflicts]
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>