Audio: Enable QCOM's HW AAC encoder conditionally

- Check related system prop to enable QCOM's HW
  AAC encoder
- Use QCOM's HW AAC encoder only for supported
  channels/sample rate/bitrate.
- Use Google's SW AAC encoder if the required AAC
  audio parameter is not supported by QCOM's HW
  AAC encoder

Change-Id: Ifc2409107e48390a6268dc5d5694df8fb47f60aa