drm/i915/vlv: Make the vlv_dpio_read/vlv_dpio_write more PHY centric

vlv_dpio_read/write should be describe more in PHY centric instead of
display controller centric.
Create a enum dpio_channel for channel index and enum dpio_phy for PHY
index.  This should better to gather for upcoming platform.

v2: Rebase the code based on
drm/i915/vlv: Fix typo in the DPIO register define.

v3: Rename vlv_phy to dpio_phy_iosf_port and define additional macro
DPIO_PHY, and remove unrelated change. (Ville)

Suggested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Chon Ming Lee <chon.ming.lee@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.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 2926563..a8a5bcb 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -452,6 +452,9 @@
 #define  DPIO_SFR_BYPASS		(1<<1)
 #define  DPIO_CMNRST			(1<<0)
 
+#define DPIO_PHY(pipe)			((pipe) >> 1)
+#define DPIO_PHY_IOSF_PORT(phy)		(dev_priv->dpio_phy_iosf_port[phy])
+
 /*
  * Per pipe/PLL DPIO regs
  */