iommu: Manage driver probe deferral better

Since iommu_fwspec_init() absorbed the basic driver probe deferral
check to wait for an IOMMU to register, we may as well handle the probe
deferral timeout there as well. The current inconsistency of callers
results in client devices deferring forever on an arm64 ACPI system
where an SMMU has failed its own driver probe.

Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/41fa59f156ef8d196d08fa75c4901e6d4b12e6c4.1733406914.git.robin.murphy@arm.com


Signed-off-by: Will Deacon <will@kernel.org>