drm/i915: extract object active state flushing code

Both busy_ioctl and the new wait_ioct need to do the same dance (or at
least should). Some slight changes:
- busy_ioctl now unconditionally checks for olr. Before emitting a
  require flush would have prevent the olr check and hence required a
  second call to the busy ioctl to really emit the request.
- the timeout wait now also retires request. Not really required for
  abi-reasons, but makes a notch more sense imo.

I've tested this by pimping the i-g-t test some more and also checking
the polling behviour of the wait_rendering_timeout ioctl versus what
busy_ioctl returns.

v2: Too many people complained about unplug, new color is
flush_active.

v3: Kill the comment about the unplug moniker.

v4: s/un-active/inactive/

Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>