drm/i915: Restrict gen6_reset_rps_interrupts to gen6+

Do not call gen6_reset_rps_interrupts() when we know the registers do not
exist.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180812223642.24865-2-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/intel_pm.c

@@ -8260,7 +8260,7 @@ void intel_sanitize_gt_powersave(struct drm_i915_private *dev_priv)
 
 	if (INTEL_GEN(dev_priv) >= 11)
 		gen11_reset_rps_interrupts(dev_priv);
-	else
+	else if (INTEL_GEN(dev_priv) >= 6)
 		gen6_reset_rps_interrupts(dev_priv);
 }