multi-arfcn, trx: add multi-channel radio I/O backend
multi-arfcn, trx: add multi-channel radio I/O backend

This implementation of the radio interface push and pull
operations runs a high rate sample stream through a
resampling channelizer to transparently present 'M'
channels to the radio interface. New channelizer and
synthesis filter classes are used for this task.

Signed-off-by: Thomas Tsou <7360a69f2d05d24df84c29f24b488ef8cc0e7ae2@vt.edu>

0x7678/openbts-multi-arfcn,0x7678/openbts-multi-arfcn,0x7678/openbts-multi-arfcn,0x7678/openbts-multi-arfcn,0x7678/openbts-multi-arfcn