allocator: Add a basic resource allocation crate

This is based on the crosvm resource allocator from commit 107edb3e.
We only have PIO and MMIO address space to handle, and don't have a GPU
specific path and space.
Also, we support allocating a range at a specified address. This is
mostly useful for PIO, but might be also necessary for MMIO.

Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

vm-allocator/src/lib.rs

@@ -0,0 +1,18 @@
+// Copyright 2018 The Chromium OS Authors. All rights reserved.
+// Copyright © 2019 Intel Corporation
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+//
+// Portions Copyright 2017 The Chromium OS Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the THIRD-PARTY file.
+
+//! Manages system resources that can be allocated to VMs and their devices.
+
+extern crate libc;
+extern crate vm_memory;
+
+mod address;
+mod system;
+
+pub use crate::address::AddressAllocator;
+pub use crate::system::SystemAllocator;