drm/i915: don't save/restore PCH_LVDS on LPT

Because the register does not exist on LPT. The interesting fact is
that reading/writing PCH_LVDS on LPT does *not* give us "unclaimed
register" messages, but the register value is always 0.
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_suspend.c

@@ -209,6 +209,7 @@ static void i915_save_display(struct drm_device *dev)
 		dev_priv->regfile.saveBLC_PWM_CTL2 = I915_READ(BLC_PWM_PCH_CTL2);
 		dev_priv->regfile.saveBLC_CPU_PWM_CTL = I915_READ(BLC_PWM_CPU_CTL);
 		dev_priv->regfile.saveBLC_CPU_PWM_CTL2 = I915_READ(BLC_PWM_CPU_CTL2);
+		if (HAS_PCH_IBX(dev) || HAS_PCH_CPT(dev))
 			dev_priv->regfile.saveLVDS = I915_READ(PCH_LVDS);
 	} else {
 		dev_priv->regfile.savePP_CONTROL = I915_READ(PP_CONTROL);
@@ -271,9 +272,9 @@ static void i915_restore_display(struct drm_device *dev)
 	if (drm_core_check_feature(dev, DRIVER_MODESET))
 		mask = ~LVDS_PORT_EN;
 
-	if (HAS_PCH_SPLIT(dev)) {
+	if (HAS_PCH_IBX(dev) || HAS_PCH_CPT(dev))
 		I915_WRITE(PCH_LVDS, dev_priv->regfile.saveLVDS & mask);
-	} else if (IS_MOBILE(dev) && !IS_I830(dev))
+	else if (INTEL_INFO(dev)->gen <= 4 && IS_MOBILE(dev) && !IS_I830(dev))
 		I915_WRITE(LVDS, dev_priv->regfile.saveLVDS & mask);
 
 	if (!IS_I830(dev) && !IS_845G(dev) && !HAS_PCH_SPLIT(dev))