ide: add ide_queue_pc_tail() helper

* Add ide_queue_pc_tail() and convert ide-{floppy,tape}.c to use it
  instead of ide*_queue_pc_tail().

* Remove no longer used ide*_queue_pc_tail().

There should be no functional changes caused by this patch.

Acked-by: Borislav Petkov <petkovbb@gmail.com>
Acked-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>