dpll: add reference-sync netlink attribute

dpll: add reference-sync netlink attribute

Add new netlink attribute to allow user space configuration of reference
sync pin pairs, where both pins are used to provide one clock signal
consisting of both: base frequency and sync signal.

Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Reviewed-by: Milena Olech <milena.olech@intel.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Arkadiusz Kubalewski <arkadiusz.kubalewski@intel.com>
Link: https://patch.msgid.link/20250626135219.1769350-2-arkadiusz.kubalewski@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>