libstagefright: Reset the decoder while performing seek

-Noise is observed when seeking to beginning of recorded AMR clip.
-While performing seek, the AMR decoder states are not being reset.
In AMR decoder, the current frame output is predicted using the states
from previous frame. If these states are not cleared, it might cause
noise when seek is performed.
-Fixed by resetting the decoder when seek is issued and port flush
completion is notified to the decoder.
Reset functions are different for AMRWB and AMRNB. Ensure to check
for mode and call appropriate reset function.

original commit -
Ibf0ebc7b154ff4866211eaf178a447f96e33341c
Ia8480b88521abc09c8b01d6052df4730a0359518

Change-Id: Ic71a014f9a87ebfe5b8520d44420716f7099f5e7