drm/i915: PSR VLV/CHV: Remove condition checks that only applies to Haswell.

These conditions applies only to Haswell and we were also checking for them
on Valleyview/Cherryview.

Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Durgadoss R <durgadoss.r@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>