Partially revert "drm/i915: tune the RC6 threshold for stability"

This reverts commit 351aa5666d02062b52329bcfe4bcf9d1f882fba9.

It breaks rc6 on at least one snb machine. Since we don't yet have a
report for ivb let's keep it there for now.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=71656
Cc: Stéphane Marchesin <marcheu@chromium.org>
Cc: erik@vontaene.de
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_pm.c

@@ -3888,7 +3888,7 @@ static void gen6_enable_rps(struct drm_device *dev)
 
 	I915_WRITE(GEN6_RC_SLEEP, 0);
 	I915_WRITE(GEN6_RC1e_THRESHOLD, 1000);
-	if (INTEL_INFO(dev)->gen <= 6 || IS_IVYBRIDGE(dev))
+	if (IS_IVYBRIDGE(dev))
 		I915_WRITE(GEN6_RC6_THRESHOLD, 125000);
 	else
 		I915_WRITE(GEN6_RC6_THRESHOLD, 50000);