iommu/arm-smmu: handle multi-alias IOMMU groups for PCI devices

IOMMU groups for PCI devices can correspond to multiple DMA aliases due
to things like ACS and PCI quirks.

This patch extends the ARM SMMU ->add_device callback so that we
consider all of the DMA aliases for a PCI IOMMU group, rather than
creating a separate group for each Requester ID.

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