drm/i915: Single thread force wake isn't used on HSW anymore

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: NVille Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_pm.c

@@ -4271,21 +4271,14 @@ static void __gen6_gt_force_wake_reset(struct drm_i915_private *dev_priv)
 
 static void __gen6_gt_force_wake_get(struct drm_i915_private *dev_priv)
 {
-	u32 forcewake_ack;
-
-	if (IS_HASWELL(dev_priv->dev))
-		forcewake_ack = FORCEWAKE_ACK_HSW;
-	else
-		forcewake_ack = FORCEWAKE_ACK;
-
-	if (wait_for_atomic((I915_READ_NOTRACE(forcewake_ack) & 1) == 0,
+	if (wait_for_atomic((I915_READ_NOTRACE(FORCEWAKE_ACK) & 1) == 0,
 			    FORCEWAKE_ACK_TIMEOUT_MS))
 		DRM_ERROR("Timed out waiting for forcewake old ack to clear.\n");
 
 	I915_WRITE_NOTRACE(FORCEWAKE, 1);
 	POSTING_READ(ECOBUS); /* something from same cacheline, but !FORCEWAKE */
 
-	if (wait_for_atomic((I915_READ_NOTRACE(forcewake_ack) & 1),
+	if (wait_for_atomic((I915_READ_NOTRACE(FORCEWAKE_ACK) & 1),
 			    FORCEWAKE_ACK_TIMEOUT_MS))
 		DRM_ERROR("Timed out waiting for forcewake to ack request.\n");