virtio-devices, vmm: Move to ExternalDmaMapping from vm-device

Now that ExternalDmaMapping is defined in vm-device, let's use it from
there.

This commit also defines the function get_host_address_range() to move
away from the vfio-ioctls dependency.

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

virtio-devices/src/iommu.rs

@@ -22,7 +22,7 @@ use std::result;
 use std::sync::atomic::AtomicBool;
 use std::sync::{Arc, Barrier, RwLock};
 use std::thread;
-use vfio_ioctls::ExternalDmaMapping;
+use vm_device::dma_mapping::ExternalDmaMapping;
 use vm_memory::{
     Address, ByteValued, Bytes, GuestAddress, GuestAddressSpace, GuestMemoryAtomic,
     GuestMemoryError, GuestMemoryMmap,