drm/i915: WARN if !HAS_PC8 when enabling/disabling PC8

We already have some checks and shouldn't be reaching these places on
!HAS_PC8 platforms, but add a WARN,  just in case.
Signed-off-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: NRodrigo Vivi <rodrigo.vivi@gmail.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -6638,6 +6638,8 @@ void hsw_enable_pc8_work(struct work_struct *__work)
 	struct drm_device *dev = dev_priv->dev;
 	uint32_t val;
 
+	WARN_ON(!HAS_PC8(dev));
+
 	if (dev_priv->pc8.enabled)
 		return;
 
@@ -6683,6 +6685,8 @@ static void __hsw_disable_package_c8(struct drm_i915_private *dev_priv)
 	if (dev_priv->pc8.disable_count != 1)
 		return;
 
+	WARN_ON(!HAS_PC8(dev));
+
 	cancel_delayed_work_sync(&dev_priv->pc8.enable_work);
 	if (!dev_priv->pc8.enabled)
 		return;