dpll: Allow associating dpll pin with a firmware node

dpll: Allow associating dpll pin with a firmware node

Extend the DPLL core to support associating a DPLL pin with a firmware
node. This association is required to allow other subsystems (such as
network drivers) to locate and request specific DPLL pins defined in
the Device Tree or ACPI.

* Add a .fwnode field to the struct dpll_pin
* Introduce dpll_pin_fwnode_set() helper to allow the provider driver
  to associate a pin with a fwnode after the pin has been allocated
* Introduce fwnode_dpll_pin_find() helper to allow consumers to search
  for a registered DPLL pin using its associated fwnode handle
* Ensure the fwnode reference is properly released in dpll_pin_put()

Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Reviewed-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>
Signed-off-by: Ivan Vecera <ivecera@redhat.com>
Reviewed-by: Arkadiusz Kubalewski <arkadiusz.kubalewski@intel.com>
Link: https://patch.msgid.link/20260203174002.705176-2-ivecera@redhat.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>