iommu/arm-smmu: Convert DMA buffer allocations to the managed API

The ARM SMMUv3 driver uses dma_{alloc,free}_coherent to manage its
queues and configuration data structures.

This patch converts the driver to the managed (dmam_*) API, so that
resources are freed automatically on device teardown. This greatly
simplifies the failure paths and allows us to remove a bunch of
handcrafted freeing code.

Signed-off-by: Will Deacon <will.deacon@arm.com>