ide-{floppy,tape}: merge pc->idefloppy_callback and pc->idetape_callback

Merge pc->idefloppy_callback and pc->idetape_callback into pc->callback.

There should be no functional changes caused by this patch.

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