drm/i915: s/GRAPHICS_VER/DISPLAY_VER/ where appropriate

Use DISPLAY_VER rather than GRAPHICS_VER to determine
availability of display hardware features.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220124193136.2397-1-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>