CSTM IQE interfaces: Simultaneous E1 and E3 channelization in a single STM-1

Supported platforms enable the mixing of E3 and E1 channels under the same cau4 interface. This is useful for a Channelized SDH interface (cstm1) with only one cau4. You can operate both e3 and e1/ce1 simultaneously on one cstm1 interface.