drm/i915: make a few DDI functions static

We don't need to export them since they're not being used outside the
file. The next time I try to find the callers for these things I will
know I won't need to look outside intel_ddi.c.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1490907472-10883-1-git-send-email-paulo.r.zanoni@intel.com
diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
index 83abab9..0914ad9 100644
--- a/drivers/gpu/drm/i915/intel_ddi.c
+++ b/drivers/gpu/drm/i915/intel_ddi.c
@@ -539,7 +539,7 @@ intel_ddi_get_buf_trans_fdi(struct drm_i915_private *dev_priv,
  * values in advance. This function programs the correct values for
  * DP/eDP/FDI use cases.
  */
-void intel_prepare_dp_ddi_buffers(struct intel_encoder *encoder)
+static void intel_prepare_dp_ddi_buffers(struct intel_encoder *encoder)
 {
 	struct drm_i915_private *dev_priv = to_i915(encoder->base.dev);
 	u32 iboost_bit = 0;
@@ -806,7 +806,7 @@ void hsw_fdi_link_train(struct intel_crtc *crtc,
 		   DP_TP_CTL_ENABLE);
 }
 
-void intel_ddi_init_dp_buf_reg(struct intel_encoder *encoder)
+static void intel_ddi_init_dp_buf_reg(struct intel_encoder *encoder)
 {
 	struct intel_dp *intel_dp = enc_to_intel_dp(&encoder->base);
 	struct intel_digital_port *intel_dig_port =
@@ -1616,8 +1616,8 @@ uint32_t ddi_signal_levels(struct intel_dp *intel_dp)
 	return DDI_BUF_TRANS_SELECT(level);
 }
 
-void intel_ddi_clk_select(struct intel_encoder *encoder,
-			  struct intel_shared_dpll *pll)
+static void intel_ddi_clk_select(struct intel_encoder *encoder,
+				 struct intel_shared_dpll *pll)
 {
 	struct drm_i915_private *dev_priv = to_i915(encoder->base.dev);
 	enum port port = intel_ddi_get_encoder_port(encoder);