system/core: don't only include dolby subformats for qcom hardware

this fixed build for devices witch use AUDIO_FORMAT_PCM_SUB_24_BIT
but don't have qcom hardware enabled for whatever reason.
put BOARD_USES_DOLBY_SUBFORMAT := true in your boardconfig

ps2: make a local variable
ps3: edit commit message
Change-Id: I4670fecfa636a90d18e6604b34029cbc2f952785