boardconfig: using BOARD_HAVE_HTC_CSDCLIENT flag for BTSco

This way audio-caf ALSADevice will use the special BTSco
csd rx/tx acdb ids, fixing RX distortion.
Doesn't fix TX distortion.

Needs: http://review.cyanogenmod.org/43541

Change-Id: Id90d2de9684d89a76741e1d8c762d48263267dc0