drm/i915/wm: warn about ilk_wm_sanitize() on display ver 9+

The sanitization should be limited to PCH split platforms up to display
version 8. Warn and bail out otherwise.

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/20230215141910.433043-2-jani.nikula@intel.com