Fix AAC bitrate computation and add missing parameters

* Compute the AAC codec bitrate based on the MTU and the AAC
  object type such that the AAC frames are not fragmented.
  The spec recommendation is to avoid fragmentation, and
  some sink devices cannot process fragmented frames.

* Setup/assign AACENC_PEAK_BITRATE as the peak bitrate to
  make sure we never go over the MTU frame size.

* Add missing AAC parameter setup for AACENC_AUDIOMUXVER
  and AACENC_SIGNALING_MODE

* Add a fix for selecting the bitrate if the sink device reports
  capability with zero bitrate - for such devices we negotiate
  our bitrate. For the actual AAC codec bitrate we still compute
  it based on the MTU and the AAC object type.

Test: Tested with numerous AAC sink devices
Bug: 34953385
Change-Id: I9ca6353b0e1ee107f1242803de4e82d568a3394b