fc-shell TCH DL handler: add support for CSD modes TCH DL capture mechanism in FC Tourmaline firmware has been extended to support CSD modes in addition to speech - add the necessary support on the host tools side. It needs to be noted that this mechanism in its present state does NOT provide the debug utility value that was sought: as we learned only after the code was implemented, TI's DSP has a misfeature in that the buffer we are reading (a_dd_0[]) is zeroed out when the IDS block is enabled, i.e., we are reading all zeros and not the real DL bits we were after. But since the code has already been written, we are keeping it - perhaps we can do some tests with IDS disabled.

This host side library contains common modules for tools like fc-tmsh and
g23sh which operate asynchronously.  This code has been factored out of
fc-tmsh.