arm64: debug: add a migration test for single-step state

Test the migration of single-step state. Setup single-stepping, migrate,
and check that we are actually single-stepping.

Signed-off-by: Ricardo Koller <ricarkol@google.com>
Message-Id: <20211210165804.1623253-4-ricarkol@google.com>
Signed-off-by: Andrew Jones <drjones@redhat.com>