msm: soundrecorder: Add support for pause/resume in HW AAC mode

- Use "stopped" notification to indicate pause/resume. This avoids
  null pointer exception while playing a recently recorded file

Change-Id: Ie5782381e816f76c34677e5863c9849609089eba
Signed-off-by: quic_mqiu <quic_mqiu@codeaurora.org>