drm/i915: detect digital outputs on Haswell

Digital port detection on Haswell is indicated by the presence of a bit in
DDI_BUF_CTL for port A, and by a different register for ports B, C and D.
So we check for those bits during the initialization time and let the hdmi
function know about those.

Note that this bit does not indicates whether the output is DP or HDMI.
However, the DDI buffers can be programmed in a way that is shared between
DP/HDMI and FDI/HDMI except for PORT E.

So for now, we detect those digital outputs as being HDMI, but proper DP
support is still pending.

Note that DDI A can only drive eDP, so we do not handle it here for hdmi
initialization.

v2: simplify Haswell handling logic

v3: use generic function for handling digital outputs.

Signed-off-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 0ad1bb38..fd96ffb 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -448,6 +448,7 @@
 extern void intel_cpt_verify_modeset(struct drm_device *dev, int pipe);
 extern void intel_prepare_ddi(struct drm_device *dev);
 extern void hsw_fdi_link_train(struct drm_crtc *crtc);
+extern void intel_ddi_init(struct drm_device *dev, enum port port);
 
 /* For use by IVB LP watermark workaround in intel_sprite.c */
 extern void intel_update_watermarks(struct drm_device *dev);