Add hardware I2S

[drewnotdrew]

Adds the following:

• Full duplex I2S module
• Random receive, transmit, and full-duplex tests

The I2S module contains the following parameters:

• BIT_DEPTH: The bit depth of the codec (e.g. bits per audio sample).
• MCLK_FREQ: The MCLK frequency used for the codec and interface.
• BCLK_DIV: The number of MCLK cycles per BCLK cycle.
• LRCLK_DIV: The number of BCLK cycles per LRCLK cycle.

random x10 reads, x10 writes, and x10 concurrent reads + writes:

This module has not been synthesized yet because the SSM2603 codec requires an I2C module, but can still be reviewed.