applied as the attached two patches to jgarzik/libata-dev.git#alpm

open issues:

1) need to check ata_dev_set_feature() return value in 
ata_dev_set_dipm() and do something useful with it

2) as the name implies, this probably better belongs in ata_link.

3) however, the feature is tightly coupled to the host controller.  in 
theory PMP -might- do this, but I think its unlikely.  as such I was OK 
with the present arrangement.

4) there has been some discussion of software-initiated device/link 
power management, but I think this should go in, in parallel with those 
discussions.  ALPM
	* is quite self-contained
	* gives a noticable power savings

I'm definitely interested in seeing somebody pursue software-initiated 
link PM as well...

	Jeff