This patch is a first try at implementing proper IDE power management.
It's not intended to be merged as-is, there is some uglyness here or
there, it's here for comments and discussion.

The point is to pipe the power management requests through the request
queue for proper locking. Since those requests involve several
operations that have to be tied together with the queue beeing locked
for further 'user' requests, they are implemented as a state machine
with specific callbacks in the subdrivers.

The guts of the patch is the core changes. I did the actual
implementation for ide-disk & ide-cd as a way to quickly validate it (it
works), but I'm sure we want to do more than just what I implemented
here. At least it's ok for PPC, but I beleive some x86 will want you to
do more (Alan suggested reverting to PIO for example, to please some
BIOSes, though that would suck badly for suspend-to-disk, there may be
more involved regarding recovering from errors in flush too).

One thing that should probably be cleaned up is the difference between
the suspend and the resume request. I didn't want to implement 2
different request bits to avoid using too much of that bit-space, and
because most of the core handling is the same. So right now, I carry in
the special structure attached to the request, 2 fields. An int
indicating if we are doing a suspend or a resume op, and an int that is
the actual state machine step.

However, for convenience, my ide-cd and ide-disk implementation
implement resume just as different step number in the same routine...

So we could either get rid of the "int suspend" field completely and
just define 2 different ranges for "step". Or we could keep "suspend",
but then it may make sense to split the sub-driver ops in 2
(suspend/suspend_completion & resume/resume_completion).

Waiting for feedback...

Ben.