drm/i915/dp: stop caching has_hdmi_sink in struct intel_dp

Use the information stored in display info. Add intel_dp_has_hdmi_sink()
helper to access it.

v2: Rebased

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/748103fda572b3552e5bbdafb300d8508d4eeaf4.1685437500.git.jani.nikula@intel.com