drm/i915/hdmi: stop caching has_audio in struct intel_hdmi

Use the information stored in display info.

Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/710286536d6b07ba8aa068b65b2b2c0c7743220e.1685437500.git.jani.nikula@intel.com