dsp: Add frame size control parameter for AAC encoder

BT sink devices have a limitation on the packet sizes
they can receive and handle from BT sources. AAC encoder
can produce output frames which can vary in size based on
content being encoded. If frame size exceeds MTU size of
BT sink device, it will lead to incorrect decoding of
frames in BT sink.
Add a frame configuration parameter (MTU/Peak bitrate)
for AAC encoder to solve this problem.

Change-Id: Ia7795049e982400b0b3657b0b3a8990fc6920e38
Signed-off-by: Aniket Kumar Lata <alata@codeaurora.org>