x86/amd-iommu: Make iommu_flush_pages aware of multiple IOMMUs

x86/amd-iommu: Make iommu_flush_pages aware of multiple IOMMUs

This patch extends the iommu_flush_pages function to flush
the TLB entries on all IOMMUs the domain has devices on.
This basically gives up the former assumption that dma_ops
domains are only bound to one IOMMU in the system.
For dma_ops domains this is still true but not for
IOMMU-API managed domains. Giving this assumption up for
dma_ops domains too allows code simplification.
Further it splits out the main logic into a generic function
which can be used by iommu_flush_tlb too.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>