platform/x86: Move all simatic ipc drivers to the subdirectory siemens

With more files around move everything to a subdirectory. Users will
only see the several options once they enable the main one.

Suggested-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Henning Schild <henning.schild@siemens.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20230719153518.13073-4-henning.schild@siemens.com
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>