iommu/arm-smmu: Call configuration impl hook before consuming features

'cfg_probe' hook is called at the very end of configuration probing
procedure and therefore features override and workaround may become
complex like for ID register fixups. In preparation for adding Marvell
errata move 'cfg_probe' a bit earlier to have chance to adjust
the detected features before we start consuming them.

Since the Cavium quirk (the only user) does not alter features
it is safe to do so.

Suggested-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Tomasz Nowicki <tn@semihalf.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/20200715070649.18733-2-tn@semihalf.com
Signed-off-by: Will Deacon <will@kernel.org>