Using AD5754 in teensy audio library

• Dual AD5754 DAC output module for for teensy audio library
• optimised for two AD5754 d/a converters with a total of 8 output channels.
• Theoretically, will also work for a single AD5754, not tested
• This module relies on another output module to call UpdateAll(), therefor I use the TDM output module to set-up all the timing registers...

TODO:

• At 14Mhz SPI clk speed, the audio buffers are transmitted slightly faster than the period which the audio buffers are received
  • So the audio is condensed and then paused for a tiny amount of time
  • possibly slow down the transmit rate, by transmitting individual bytes at a regular interval, between data writes, without asserting the cable select, so ignored by AD5754 devices