ide-floppy: use an xfer_func_t and io_buf_t typedefs in order to unify rw

Also, move xfer_func_t typedef to the ide.h since it is used by two drivers
now (more coming).

Bart:
- use __func__ while at it

Signed-off-by: Borislav Petkov <bbpetkov@yahoo.de>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>