tests/migration: Enable the migration test on s390x, too

tests/migration: Enable the migration test on s390x, too

We can re-use the s390-ccw bios code to implement a small firmware
for a s390x guest which prints out the "A" and "B" characters and
modifies the memory, as required for the migration test.

[quintela: Converted the compile script to Makefile rules]
Signed-off-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-Id: <1539078677-25396-1-git-send-email-thuth@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
  Fixed up Makefile since the aarch patch sneaked in first