drm/i915: split intel_hdmi_init into encoder and connector pieces

We want to split the HDMI connector and encoder initialization because
in the future the DDI code will have its own "encoder init" function,
but it will still call intel_hdmi_init_connector. The DDI encoder will
actually have two connectors attached to it: HDMI and DP.

The best way to look at this patch is to imagine that we're renaming
intel_hdmi_init to intel_hdmi_init_connector and removing the
encoder-specific pieces and placing them into intel_hdmi_init.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>