mtk_pctrl_is_function_valid
ret = mtk_pctrl_is_function_valid(pctl, pin, fnum);
ret = mtk_pctrl_is_function_valid(pctl, g->pin, function);
ret = mtk_pctrl_is_function_valid(pctl, pin, fnum);
ret = mtk_pctrl_is_function_valid(hw, grp->pin, function);