drm/i915: Unduplicate CHV phy-releated pre pll enabling code

The same logic is used for DP and HDMI so move it to intel_dpio_phy.c.

v2: Rebase

Signed-off-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Reviewed-by: Jim Bride <jim.bride@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1461761065-21195-5-git-send-email-ander.conselvan.de.oliveira@intel.com
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 123f6ba..66403b5 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -3595,6 +3595,7 @@
 			      bool uniq_trans_scale);
 void chv_data_lane_soft_reset(struct intel_encoder *encoder,
 			      bool reset);
+void chv_phy_pre_pll_enable(struct intel_encoder *encoder);
 
 int intel_gpu_freq(struct drm_i915_private *dev_priv, int val);
 int intel_freq_opcode(struct drm_i915_private *dev_priv, int val);