drm/i915/alpm: Add new interface to check if AUXLess ALPM is used

we need to know if AUXLess ALPM is used when preparing for link
training. Add new interface for this and use it in existing code where
possible.

v2: remove kerneldoc comment

Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Link: https://lore.kernel.org/r/20250526120512.1702815-8-jouni.hogander@intel.com