drm/i915: Re-enable RPS wait-boosting for all engines

This reverts commit ec5cc0f9
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Thu Jun 12 10:28:55 2014 +0100

    drm/i915: Restrict GPU boost to the RCS engine

The premise that media/blitter workloads are not affected by boosting is
patently false with a trip through igt. The question that remains is
what exactly is going wrong with the media workload that prompted this?
Hopefully that would be fixed by the missing agressive downclocking, in
addition to the extra restrictions imposed on how frequent a process is
allowed to boost.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Deepak S <deepak.s@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll>
Acked-by: Deepak S <deepak.s@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>