Add DAC2 HD to device list

[Marrahm]

Drivers for the DAC2HD are already in the kernel and it works well with minimal implementation effort now (see http://moodeaudio.org/forum/showthread.php?tid=3389), but it would be great to see it added to the I2S list of devices in some future implementation.  

Thanks,
Mike

[TeronG]

Also DAC2 Pro. It uses and works with the same driver as DAC+ Pro.