drm/i915/cml: Introduce Comet Lake PCH

Comet Lake PCH is based off of Cannon Point(CNP).
Add PCI ID for Comet Lake PCH.

v2: Code cleanup (DK)

v3: Comment cleanup (Jani)

Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190318200133.9666-2-anusha.srivatsa@intel.com

drivers/gpu/drm/i915/i915_drv.c

@@ -188,6 +188,11 @@ intel_pch_type(const struct drm_i915_private *dev_priv, unsigned short id)
 		DRM_DEBUG_KMS("Found Cannon Lake LP PCH (CNP-LP)\n");
 		WARN_ON(!IS_CANNONLAKE(dev_priv) && !IS_COFFEELAKE(dev_priv));
 		return PCH_CNP;
+	case INTEL_PCH_CMP_DEVICE_ID_TYPE:
+		DRM_DEBUG_KMS("Found Comet Lake PCH (CMP)\n");
+		WARN_ON(!IS_COFFEELAKE(dev_priv));
+		/* CometPoint is CNP Compatible */
+		return PCH_CNP;
 	case INTEL_PCH_ICP_DEVICE_ID_TYPE:
 		DRM_DEBUG_KMS("Found Ice Lake PCH\n");
 		WARN_ON(!IS_ICELAKE(dev_priv));

drivers/gpu/drm/i915/i915_drv.h

@@ -537,7 +537,7 @@ enum intel_pch {
 	PCH_LPT,	/* Lynxpoint/Wildcatpoint PCH */
 	PCH_SPT,        /* Sunrisepoint PCH */
 	PCH_KBP,        /* Kaby Lake PCH */
-	PCH_CNP,        /* Cannon Lake PCH */
+	PCH_CNP,        /* Cannon/Comet Lake PCH */
 	PCH_ICP,	/* Ice Lake PCH */
 };
 
@@ -2547,6 +2547,7 @@ static inline unsigned int i915_sg_segment_size(void)
 #define INTEL_PCH_KBP_DEVICE_ID_TYPE		0xA280
 #define INTEL_PCH_CNP_DEVICE_ID_TYPE		0xA300
 #define INTEL_PCH_CNP_LP_DEVICE_ID_TYPE		0x9D80
+#define INTEL_PCH_CMP_DEVICE_ID_TYPE		0x0280
 #define INTEL_PCH_ICP_DEVICE_ID_TYPE		0x3480
 #define INTEL_PCH_P2X_DEVICE_ID_TYPE		0x7100
 #define INTEL_PCH_P3X_DEVICE_ID_TYPE		0x7000