drm/i915/display: use DISPLAY_VER() on remaining users

Commit 989634fb ("drm/i915/audio: set HDA link parameters in driver")
added INTEL_GEN() in the display code, where it should actually be using
DISPLAY_VER(). Switch to the new macro.

Cc: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210413051002.92589-2-lucas.demarchi@intel.com