audio : Fixed usage of QTI_FLAC_DECODER

QTI FLAC Decoder specific code is not placed under QTI_FLAC_DECODER
properly in some places in the framework.

Made sure that Qcom FLAC specific code is placed properly under
QTI_FLAC_DECODER, to stub out FLACDecoder on B-Family.

Change-Id: Id29d3dc262951a714c4c72cf732893589e282a76
CRs-fixed: 778723