drm/i915/display: reduce includes in intel_hdmi.h

Only include what's needed.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/5949a57979dae615731b6ff54d5d150b91e34d27.1667383630.git.jani.nikula@intel.com