drm/i915/display: Use device parameters instead of module in I915_STATE_WARN

Also make module parameter as non writable.

Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231024124109.384973-21-jouni.hogander@intel.com