audio: mute duration at the beginning of recording

-AudioSource mutes for predefined duration (kAutoRampStartUs)
 at the beginning of a recording. Current kAutoRampStartUs
 is not sufficient to mute the shutter sound click on
 B-Family devices. Sometime shutter sound is getting recorded
 with the current kAutoRampStartUs.

-Issue with calculating muteDuration from getOutputLatency is,
 more delay is getting added for Bt(~1 sec) which is really not
 required.

-Fix is to use constant mute delay which is appropriate

Change-Id: Ia2456d387f2af6da49891403d579e36b0eacfabb
CRs-Fixed: 636491
libstagefright: Fix to handle EAGAIN error on first read to source

 -Some of AV streaming clips are not played
 -In streaming use case when source does not have sufficent data it
  return error EAGAIN on first read request, player ignore this error
  and treat it as a first buffer.
 -Make the read request again to source on EAGAIN error.

Change-Id: I3feaccce757c17c4e80e6d62375c3d700ca29e72
stagefright: yield callbackDispatcher to writer only for video

Letting Writer run increases the probability of dispatcher
not getting the lock when it comes back with the next message.
This adds an extra sleep-wakeup and increase power consumption.

Since Audio dispatcher handles more messages, this behavior
is profound in case of audio. Contain yielding business to
video only since this optimization is not required for audio.

CRs-Fixed: 651233
Change-Id: Ie24be4522b29fa191a88a777293d39f8e7c91353