aec62xx: fix PIO/DMA setup issues

Teach the driver's tuneproc() method to do PIO auto-runing properly since it
treated 5 instead of 255 as auto-tune request, and also passed the mode limit
of PIO5 to ide_get_best_pio_mode() despite supporting up to PIO4 only.

While at it, also:

- remove the driver's wrong claim about supporting SWDMA modes;

- stop hooking ide_dma_timeout() method as the handler clearly doesn't fit for
  the task...

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