tests: Add migration test for aarch64

tests: Add migration test for aarch64

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: Juan Quintela <[email protected]>
Reviewed-by: Andrew Jones <[email protected]>
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Tested-by: Philippe Mathieu-Daudé <[email protected]>
Signed-off-by: Wei Huang <[email protected]>
Message-Id: <1538669326[email protected]>
Signed-off-by: Dr. David Alan Gilbert <[email protected]>