ice: disallow DPLL_PIN_STATE_SELECTABLE for dpll output pins

ice: disallow DPLL_PIN_STATE_SELECTABLE for dpll output pins

Currently the user may request DPLL_PIN_STATE_SELECTABLE for an output
pin, and this would actually set the DISCONNECTED state instead.

It doesn't make any sense. SELECTABLE is valid only in case of input pins
(on AUTOMATIC type dpll), where dpll itself would select best valid input.
For the output pin only CONNECTED/DISCONNECTED are expected.

Fixes: d7999f5ea64b ("ice: implement dpll interface to control cgu")
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Reviewed-by: Paul Menzel <pmenzel@molgen.mpg.de>
Signed-off-by: Arkadiusz Kubalewski <arkadiusz.kubalewski@intel.com>
Tested-by: Pucha Himasekhar Reddy <himasekharx.reddy.pucha@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>