drm/i915/tv: use DISPLAY_VER instead of GRAPHICS_VER

Display code should not care about graphics version. It's only comments
here, but update anyway.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240104174350.823605-5-jani.nikula@intel.com