drm/i915/cfl: Coffee Lake uses CNP PCH.

So let's force it on the virtual detection.

Also it is still the only silicon for now on this PCH,
so WARN otherwise.

v2: Rebased on top of Cannonlake and added the missed
    debug message as pointed by DK.

Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1496937000-8450-2-git-send-email-rodrigo.vivi@intel.com

drivers/gpu/drm/i915/i915_drv.c

@@ -139,8 +139,9 @@ static enum intel_pch intel_virt_detect_pch(struct drm_i915_private *dev_priv)
 	} else if (IS_SKYLAKE(dev_priv) || IS_KABYLAKE(dev_priv)) {
 		ret = PCH_SPT;
 		DRM_DEBUG_KMS("Assuming SunrisePoint PCH\n");
-	} else if (IS_CANNONLAKE(dev_priv)) {
+	} else if (IS_COFFEELAKE(dev_priv) || IS_CANNONLAKE(dev_priv)) {
 		ret = PCH_CNP;
+		DRM_DEBUG_KMS("Assuming CannonPoint PCH\n");
 	}
 
 	return ret;
@@ -224,11 +225,13 @@ static void intel_detect_pch(struct drm_i915_private *dev_priv)
 			} else if (id == INTEL_PCH_CNP_DEVICE_ID_TYPE) {
 				dev_priv->pch_type = PCH_CNP;
 				DRM_DEBUG_KMS("Found CannonPoint PCH\n");
-				WARN_ON(!IS_CANNONLAKE(dev_priv));
+				WARN_ON(!IS_CANNONLAKE(dev_priv) &&
+					!IS_COFFEELAKE(dev_priv));
 			} else if (id_ext == INTEL_PCH_CNP_LP_DEVICE_ID_TYPE) {
 				dev_priv->pch_type = PCH_CNP;
 				DRM_DEBUG_KMS("Found CannonPoint LP PCH\n");
-				WARN_ON(!IS_CANNONLAKE(dev_priv));
+				WARN_ON(!IS_CANNONLAKE(dev_priv) &&
+					!IS_COFFEELAKE(dev_priv));
 			} else if ((id == INTEL_PCH_P2X_DEVICE_ID_TYPE) ||
 				   (id == INTEL_PCH_P3X_DEVICE_ID_TYPE) ||
 				   ((id == INTEL_PCH_QEMU_DEVICE_ID_TYPE) &&