iommu/arm-smmu: Clean up early-probing workarounds

Now that the appropriate ordering is enforced via profe-deferral of
masters in core code, rip it all out and bask in the simplicity.

Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
[Sricharan: Rebased on top of ACPI IORT SMMU series]
Signed-off-by: Sricharan R <sricharan@codeaurora.org>