ieee1394: sbp2: add workarounds for 2nd and 3rd generation iPods

as per https://bugs.launchpad.net/bugs/294391.  These got one sample of
each iPod generation going.  However there still occurred I/O stalls
with the 3rd generation iPod which remain undiagnosed at the time of
this writing.

Acked-by: Jarod Wilson <jarod@redhat.com>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>