Add support for playing audio during bootanimation

The bootanimation daemon will play 16 bit WAV files contained in bootanimation.zip
For this to work, the bootanimation.zip must contain an audio_conf.txt file,
which contains parameters to be used for the tinyalsa pcm_open call
as well as mixer parameters to set before attempting to play the sound.

If the bootanimation finds an audio_conf.txt file, then it will look for a file named
"audio.wav" in each of the part subdirectories. If audio.wav is found, it will play that
WAV file starting at the beginning of that part.

The code for this is based on the tinyplay utility in tinyalsa.

The audio_conf.txt and must begin with the following header:

card=<ALSA card number>
device=<ALSA device number>
period_size=<period size>
period_count=<period count>

This header is followed by zero or more mixer settings, each with the format:
mixer "<name>" = <value list>
Since mixer names can contain spaces, the name must be enclosed in double quotes.
The values in the value list can be integers, booleans (represented by 0 or 1)
or strings for enum values.

Finally I should mention that this change is not the right approach.
Instead of going straight to ALSA we should be using the mediaserver instead.
But mediaserver isn't ready in time due to interactions with the system server, and there
isn't time to fix this for the current release. We need to fix that for the next one.

Bug: 17674304

Change-Id: Ic391ade61c941d0a24f4d64fe005ac9375a23fa9