AudioOutputSPDIF3::config_spdif3() used to configure spdif receiver

https://forum.pjrc.com/threads/28639-S-pdif?p=159530&viewfull=1#post159530

One write was out-of-bounds due to worng address put (I was using the
device address rather than the register address), another write
overwrote the Power Management register with the Mode Control register.
Now everything works. Added two exampes: SineOutTest that puts two
sinewaves on the outputs, and PassthroughTest that connects the two
inputs to the two outputs.

The PIN_PDN was not set as output, therefore it would not transition to
LOW for 150 ns and then stay HIGH to properly enable the CODEC. The
CODEC now powers up, at least.

The test puts a 440 Hz sinewave on one channel, and a 220 Hz on the
other

https://forum.pjrc.com/threads/27409-Play-RAW-from-Serial-Flash?p=77666#post77666