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. This is causing an issue for
the customer who has their own FLACDecoder.

Made sure that Qcom FLAC specific code is placed properly under
QTI_FLAC_DECODER

Change-Id: Ifc49f86643412095682477f35659760b228ec633
CRs-fixed: 769129