drm/i915: Move has_hdmi_sink out from intel_hdmi_compute_config()

We'll be wanting to compute has_hdmi_sink a bit differently
for some platforms. To that end compute it in the encoder
.compute_config_hook() before we call intel_hdmi_compute_config().
intel_hdmi_compute_has_hdmi_sink() will do the basic lifting
beyond any platform specific stuff.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221107194604.15227-5-ville.syrjala@linux.intel.com


Reviewed-by: Jani Nikula <jani.nikula@intel.com>