HEADSUP! ATA driver changes for (modern) Promise controllers

Beware if you have Promise controller that fit this, support is new and 
may be fragile :) let me know if there are problems....

The commit log says it all:

Add support for the Promise command sequencer present on all modern 
Promise controllers (PDC203** PDC206**).

This also adds preliminary support for the Promise SX4/SX4000 but *only* 

as a "normal" Promise ATA controller (ATA RAID's are supported though
but only RAID0, RAID1 and RAID0+1).

This cuts off yet another 5-8% of the command overhead on promise 
controllers, making them the fastest we have ever had support for.

Work is now continuing to add support for this in ATA RAID, to 
accellerate ATA RAID quite a bit on these controllers, and especially 
the SX4/SX4000 series as they have quite a few tricks in there..

This commit also adds a few fixes to the SATA code needed for proper 
support.

-- 
-Søren