Make helper functions private

source/private/bitfield2input.m

source/private/bitfield2port.m

source/private/bool2str.m

source/private/brake2str.m

source/private/input2bitfield.m

source/private/input2port.m

source/private/isBool.m

source/private/isCommInterfaceValid.m

source/private/isDeviceValid.m

source/private/isModeValid.m

source/private/isPortEnumValid.m

source/private/isPortStrValid.m

source/private/isSyncedBitfield.m

source/private/port2bitfield.m

source/private/port2input.m

source/private/port2str.m

source/private/str2PortParam.m

source/private/str2bool.m

source/private/str2brake.m