cloud-hypervisor: Add the architecture crates

Both crates are based on Firecracker commit 9cdb5b2.
They are ported to the new memory model and tests have been fixed
accordingly.

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

arch_gen/src/lib.rs

@@ -0,0 +1,5 @@
+// Copyright 2018 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+#[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
+pub mod x86;