drm/i915: Pixel Clock changes for DSI dual link

For dual link MIPI Panels, each port needs half of pixel clock. Pixel overlap
can be enabled if needed by panel, then in that case, pixel clock will be
increased for extra pixels.

v2 : Address review comments by Jani
     - Removed the bit mask used for ->dual_link
     - Used DSI instead of MIPI for #define variables

v3: Added the VLV_DISPLAY_BASE to VLV_CHICKEN_3 register

Signed-off-by: Gaurav K Singh <gaurav.k.singh@intel.com>
Signed-off-by: Shobhit Kumar <shobhit.kumar@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index b4a11ab..869e5ae 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -6030,6 +6030,10 @@
 #define GEN8_PMINTR_REDIRECT_TO_NON_DISP	(1<<31)
 #define VLV_PWRDWNUPCTL				0xA294
 
+#define VLV_CHICKEN_3				(VLV_DISPLAY_BASE + 0x7040C)
+#define  PIXEL_OVERLAP_CNT_MASK			(3 << 30)
+#define  PIXEL_OVERLAP_CNT_SHIFT		30
+
 #define GEN6_PMISR				0x44020
 #define GEN6_PMIMR				0x44024 /* rps_lock */
 #define GEN6_PMIIR				0x44028