dpll: add phase-offset-monitor feature to netlink spec

dpll: add phase-offset-monitor feature to netlink spec

Add enum dpll_feature_state for control over features.

Add dpll device level attribute:
DPLL_A_PHASE_OFFSET_MONITOR - to allow control over a phase offset monitor
feature. Attribute is present and shall return current state of a feature
(enum dpll_feature_state), if the device driver provides such capability,
otherwie attribute shall not be present.

Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@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>
Acked-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>
Link: https://patch.msgid.link/20250612152835.1703397-2-arkadiusz.kubalewski@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>