ice: dpll: fix output pin capabilities

The dpll output pins which are used to feed clock signal of PHY and MAC
circuits cannot be disconnected, those integrated circuits require clock
signal for operation.
By stopping assignment of DPLL_PIN_CAPABILITIES_STATE_CAN_CHANGE pin
capability, prevent the user from invoking the state set callback on
those pins, setting the state on those pins already returns error, as
firmware doesn't allow the change of their state.

Fixes: d7999f5e ("ice: implement dpll interface to control cgu")
Fixes: 8a3a565f

 ("ice: add admin commands to access cgu configuration")
Reviewed-by: Andrii Staikov <andrii.staikov@intel.com>
Signed-off-by: Arkadiusz Kubalewski <arkadiusz.kubalewski@intel.com>
Tested-by: Sunitha Mekala <sunithax.d.mekala@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>