[Intel-gfx] [RFC] Runtime display PM for VLV/BYT

[Jesse Barnes]

This set adds bits needed for runtime power support, currently only
lightly tested on VLV/BYT:
  1) suspend/resume callbacks for different platforms
  2) save/restore of display state across a power well toggle
  3) get/put of display power well in critical places

The TODO list still has a few items on it, and I'm looking for feedback:
  1) sprinkle around some power well WARNs so we can catch things easily
  2) add some tests using DPMS and NULL mode sets and comparing power
     well state
  3) better debugfs support for multiple wells
  4) refcount of power well in debugfs (with ref holders?)
  5) more testing - I think the load time ref is still busted here and
     on HSW
  6) convert HSW as well so DPMS will shut things down, not just mode
     sets

Thoughts or comments?

Thanks,
Jesse