alsa_sound: add HTC CSD CLIENT board flag for special cases (BT)

New HTC phones like m7 have special settings for BTSco CSD device
ids. Adding board flag BOARD_HAVE_HTC_CSDCLIENT to handle
these special cases related to HTC's csd client.

Change-Id: Iae3cb4568c0d1d6b5d75cef7a836d78ab3fa9522