drm/i915/cnl: Add max allowed Cannonlake DC.

This is a follow-up after enabling DC states with
commit: "drm/i915/DMC/CNL: Load DMC on CNL".

Cc: Anusha Srivatsa <anusha.srivatsa@intel.com>
Cc: Imre Deak <imre.deak@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1499373908-26761-1-git-send-email-rodrigo.vivi@intel.com

drivers/gpu/drm/i915/intel_runtime_pm.c

@@ -2492,7 +2492,7 @@ static uint32_t get_allowed_dc_mask(const struct drm_i915_private *dev_priv,
 	int requested_dc;
 	int max_dc;
 
-	if (IS_GEN9_BC(dev_priv)) {
+	if (IS_GEN9_BC(dev_priv) || IS_CANNONLAKE(dev_priv)) {
 		max_dc = 2;
 		mask = 0;
 	} else if (IS_GEN9_LP(dev_priv)) {