drm/i915/alpm: Move port alpm configuration

It is specified in Bspec where port alpm configuration is supposed to be
performed. Change accordingly.

v2:
  - drop HAS reference
  - ensure PORT_ALPM registers are not writen on older platform

Bspec: 68849
Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Link: https://lore.kernel.org/r/20250526120512.1702815-9-jouni.hogander@intel.com