it to determine the boot device: mvme68k, pc532, macppc, ofppc. Those
platforms should be changed to use device_register(). In the mean time,
those ports defined __BROKEN_DK_ESTABLISH.
- Make synchronous writes optional, disabled by default (*way* too slow).
- Handle case where dm_nsegs > CAC_SG_SIZE.
- Fix a couple of silly bugs.
- Fix use of __attribute__((__packed__));