tests/acceptance: Move the pseries test to a separate file

Let's gather the POWER-related tests in a separate file.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Wainer dos Santos Moschetta <wainersm@redhat.com>
Reviewed-by: Willian Rampazzo <willianr@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Acked-by: David Gibson <david@gibson.dropbear.id.au>
Message-Id: <20210112164045.98565-2-thuth@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>