drm/i915: Fix up PSR frontbuffer tracking

drm/i915: Fix up PSR frontbuffer tracking

I've tried to split this up, but all the changes are so tightly
related that I didn't find a good way to do this without breaking
bisecting. Essentially this completely changes how psr is glued into
the overall driver, and there's not much you can do to soften such a
paradigm change.

- Use frontbuffer tracking bits stuff to separate disable and
  re-enable.

- Don't re-check everything in the psr work. We have now accurate
  tracking for everything, so no need to check for sprites or tiling
  really. Allows us to ditch tons of locks.

- That in turn allows us to properly cancel the work in the disable
  function - no more deadlocks.

- Add a check for HSW sprites and force a flush. Apparently the
  hardware doesn't forward the flushing when updating the sprite base
  address. We can do the same trick everywhere else we have such
  issues, e.g. on baytrail with ... everything.

- Don't re-enable psr with a delay in psr_exit. It really must be
  turned off forever if we detect a gtt write. At least with the
  current frontbuffer render tracking. Userspace can do a busy ioctl
  call or no-op pageflip to re-enable psr.

- Drop redundant checks for crtc and crtc->active - now that they're
  only called from enable this is guaranteed.

- Fix up the hsw port check. eDP can also happen on port D, but the
  issue is exactly that it doesn't work there. So an || check is
  wrong.

- We still schedule the psr work with a delay. The frontbuffer
  flushing interface mandates that we upload the next full frame, so
  need to wait a bit. Once we have single-shot frame uploads we can do
  better here.

v2: Don't enable psr initially, rely upon the fb flush of the initial
plane setup for that. Gives us more unified code flow and makes the
crtc enable sequence less a special case.

v3: s/psr_exit/psr_invalidate/ for consistency

v4: Fixup whitespace.

v5: Correctly bail out of psr_invalidate/flush when
dev_priv->psr.enabled is NULL. Spotted by Rodrigo.

v6:
- Only schedule work when there's work to do. Fixes WARNINGs reported
  by Rodrigo.
- Comments Chris requested to clarify the code.

v7: Fix conflict on rebase (Rodrigo)

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch> (v6)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>