Developing I2S module for uPy

[blmorris]

For now I have just put the checks in place, but I keep thinking that there is a better way if only I understood the code better.
I should have an early version of my I2S code to post in a few days, so I'll find out if I've done anything really goofy then.

[blmorris]

I have just posted my (very!) preliminary I2S code: https://github.com/blmorris/micropython/tree/stm-i2s

I would welcome any comments, critiques or discussion here or at https://github.com/micropython/micropython/issues/1165

Currently I have implemented a dynamic I2S object modelled on uart.c and can.c; the I2S object can initialize and configure the I2S hardware, but send and receive methods are not yet implemented.
-Bryan