As part of splitting-out DMAR busdma backend, rename:
DMAR_LOCK -> IOMMU_LOCK
DMAR_ASSERT_LOCKED
dmar_unit -> iommu_unit
dmar_domain -> iommu_domain
dmar_ctx -> iommu_device
dmar_map_entry->iommu_map_entry
DMAR_MAP_ENTRY*->IOMMU_MAP_ENTRY*
dmar_test_boundary -> iommu_test_boundary
ctx_tag -> device_tag
DMAR_GM -> IOMMU_MF
DMAR_DOMAIN -> IOMMU_DOMAIN
dmar_get_requester -> iommu_get_requester
dmar_bus_dma_is_dev_disabled -> iommu_bus_dma_is_dev_disabled
dmar_instantiate_ctx -> iommu_instantiate_device
dmar_bus_* -> iommu_bus_*
bus_dma_tag_dmar -> bus_dma_tag_iommu
bus_dmamap_dmar -> bus_dmamap_iommu
BUS_DMAMAP_DMAR* -> BUS_DMAMAP_IOMMU*
dmar_init_busdma -> iommu_init_busdma
dmar_fini_busdma -> iommu_fini_busdma
dmar_map_entries_tailq -> iommu_map_entries_tailq
bus_dma_dmar_impl -> bus_dma_iommu_impl