dpll: zl3073x: Add support for mux pin type

dpll: zl3073x: Add support for mux pin type

Add parsing for the "mux" string in the 'connection-type' pin property
mapping it to DPLL_PIN_TYPE_MUX.

Recognizing this type in the driver allows these pins to be taken as
parent pins for pin-on-pin pins coming from different modules (e.g.
network drivers).

Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Signed-off-by: Ivan Vecera <ivecera@redhat.com>
Reviewed-by: Arkadiusz Kubalewski <arkadiusz.kubalewski@intel.com>
Link: https://patch.msgid.link/20260203174002.705176-6-ivecera@redhat.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>