ExtendedCodec: update amrwb+ format parameters

- Add new API to update channel count and
  sample rate of Amrwb+ format.

CRs-Fixed: 631469

Change-Id: I46d2f219a13f3edf49ac0e7a8d098ca96bcd22a2
stagefright: ExtendedCodec: enable arbitrary/frame-by-frame mode

Based on the parser's hint, explicitly enable arbitrary or frame-
by-frame mode rather than assume component's default mode.

Change-Id: I0931b84f3757625d1e62311c2171ff48defcbe04
CRs-Fixed: 642025