i2s: Add WAV dump support, drop obsolete 'i2s_dump' PD.

i2s: Add WAV dump support, drop obsolete 'i2s_dump' PD.

The functionality of the preliminary 'i2s_dump' PD is now available
in the proper 'i2s' PD, via the OUTPUT_BINARY mechanism that frontends
can use to dump decoded data (in various formats) to a file, or pipe it
into other applications, and so on.

Old sigrok-cli example usage:

 $ sigrok-cli -i 2ch-16bit-16khz.sr \
	-P i2s:sck=0:ws=1:sd=2,i2s_dump:filename=foo.wav
 $ aplay foo.wav

New sigrok-cli example usage:

 $ sigrok-cli -i 2ch-16bit-16khz.sr \
	-P i2s:sck=0:ws=1:sd=2 -B i2s=wav > foo.wav
 $ aplay foo.wav

New sigrok-cli example usage (piping into other applications):

 $ sigrok-cli -i 2ch-16bit-16khz.sr \
	-P i2s:sck=0:ws=1:sd=2 -B i2s=wav | aplay -