ide: add ide_do_start_stop() helper

* Add ide_do_start_stop() helper and convert ide-{floppy,tape}.c
  to use it.

* Remove no longer used idefloppy_create_start_stop_cmd()
  and idetape_create_load_unload_cmd().

There should be no functional changes caused by this patch.

Acked-by: Borislav Petkov <petkovbb@gmail.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>