vm-device: Move ExternalDmaMapping trait out of vfio-ioctls

By moving the trait and its VFIO implementation out of vfio-ioctls, we
give anticipate for the move to the vfio-ioctls from rust-vmm.

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

vm-device/src/dma_mapping/mod.rs

@@ -0,0 +1,17 @@
+// Copyright © 2021 Intel Corporation
+//
+// SPDX-License-Identifier: Apache-2.0 OR BSD-3-Clause
+
+pub mod vfio;
+
+/// Trait meant for triggering the DMA mapping update related to an external
+/// device not managed fully through virtio. It is dedicated to virtio-iommu
+/// in order to trigger the map update anytime the mapping is updated from the
+/// guest.
+pub trait ExternalDmaMapping: Send + Sync {
+    /// Map a memory range
+    fn map(&self, iova: u64, gpa: u64, size: u64) -> std::result::Result<(), std::io::Error>;
+
+    /// Unmap a memory range
+    fn unmap(&self, iova: u64, size: u64) -> std::result::Result<(), std::io::Error>;
+}