iommu/msm: Claim bus ops on probe

Since the MSM IOMMU driver now probes via DT exclusively rather than
platform data, dependent masters should be deferred until the IOMMU
itself is ready. Thus we can do away with the early initialisation
hook to unconditionally claim the bus ops, and instead do that only
once an IOMMU is actually probed. Furthermore, this should also make
the driver safe for multiplatform kernels on non-MSM SoCs.

Reviewed-by: Sricharan R <sricharan@codeaurora.org>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>