This patch adds migration test support for aarch64. The test code, which
implements the same functionality as x86, is booted as a kernel in qemu.
Here are the design choices we make for aarch64:

 * We choose this -kernel approach because aarch64 QEMU doesn't provide a
   built-in fw like x86 does. So instead of relying on a boot loader, we
   use -kernel approach for aarch64.
 * The serial output is sent to PL011 directly.
 * The physical memory base for mach-virt machine is 0x40000000. We change
   the start_address and end_address for aarch64.

In addition to providing the binary, this patch also includes the source
code and the build script in tests/migration/aarch64. So users can change
the source and/or re-compile the binary as they wish.
Reviewed-by: NJuan Quintela <quintela@redhat.com>
Reviewed-by: NAndrew Jones <drjones@redhat.com>
Reviewed-by: NPhilippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: NPhilippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: NWei Huang <wei@redhat.com>
Message-Id: <1538669326-28135-1-git-send-email-wei@redhat.com>
Signed-off-by: NDr. David Alan Gilbert <dgilbert@redhat.com>