drm/i915/chv: Add DPIO offset for Cherryview. v3

CHV has 2 display phys.  First phy (IOSF offset 0x1A) has two channels,
and second phy (IOSF offset 0x12) has single channel.  The first phy is
used for port B and port C, while second phy is only for port D.

v2: Move the pipe to determine which phy to select for
vlv_dpio_read/vlv_dpio_write to another patch. (Daniel)
v3: Rebase the code based on rework on how to calculate DPIO offset.

Signed-off-by: Chon Ming Lee <chon.ming.lee@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 5efe322..edb768a 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -92,7 +92,7 @@
 };
 #define port_name(p) ((p) + 'A')
 
-#define I915_NUM_PHYS_VLV 1
+#define I915_NUM_PHYS_VLV 2
 
 enum dpio_channel {
 	DPIO_CH0,