Kill the HSW check from the single thread force wake code. HSW
uses MT force wake exclusively these days.

The commit that removed HSW single thread forcewake support:

 commit 36ec8f87
 Author: Daniel Vetter <daniel.vetter@ffwll.ch>
 Date:   Thu Oct 18 14:44:35 2012 +0200

    drm/i915: unconditionally use mt forcewake on hsw/ivb
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>