frameworks/av: Disable multichannel FLAC and AAC subformat on Offload

-Currently, check for disabling AAC and its subformat disables
Offload on every other format which has xxxxx1xx in the most
significant byte of the mask. By comparing this result to original
AAC mask, we can ensure that only AAC and its subformat passes.
-Disable FLAC multi-channel playback on offload.

Change-Id: I0bfa829ea839b19dc4c6051b020397a1a8749c12