mixmrt/machine_i2s: Add I2S protocol support.

This commit adds support for machine.I2S on the mimxrt port.  The I2S API
is consistent with the existing stm32, esp32, and rp2 implementations.

I2S features:
- controller transmit and controller receive
- 16-bit and 32-bit sample sizes
- mono and stereo formats
- sampling frequencies from 8kHz to 48kHz
- 3 modes of operation:
  - blocking
  - non-blocking with callback
  - uasyncio
- configurable internal buffer
- optional MCK

Tested with the following development boards:
- MIMXRT1010_EVK, MIMXRT1015_EVK, MIMXRT1020_EVK, MIMXRT1050_EVK
- Teensy 4.0, Teensy 4.1
- Olimex RT1010
- Seeed ARCH MIX

Tested with the following I2S hardware peripherals:
- UDA1334
- GY-SPH0645LM4H
- WM8960 codec on board the MIMXRT boards and separate breakout board
- INMP441
- PCM5102
- SGTL5000 on the Teensy audio shield

Signed-off-by: Mike Teachman <mike.teachman@gmail.com>

docs/library/machine.I2S.rst

@@ -75,23 +75,19 @@ uasyncio::
 Constructor
 -----------
 
-.. class:: I2S(id, *, sck, ws, sd, mode, bits, format, rate, ibuf)
+.. class:: I2S(id, *, sck, ws, sd, mck=None, mode, bits, format, rate, ibuf)
 
    Construct an I2S object of the given id:
 
-   - ``id`` identifies a particular I2S bus.
-
-   ``id`` is board and port specific:
-
-     - PYBv1.0/v1.1: has one I2S bus with id=2.
-     - PYBD-SFxW: has two I2S buses with id=1 and id=2.
-     - ESP32: has two I2S buses with id=0 and id=1.
+   - ``id`` identifies a particular I2S bus; it is board and port specific
 
    Keyword-only parameters that are supported on all ports:
 
      - ``sck`` is a pin object for the serial clock line
      - ``ws`` is a pin object for the word select line
      - ``sd`` is a pin object for the serial data line
+     - ``mck`` is a pin object for the master clock line;
+       master clock frequency is sampling rate * 256
      - ``mode`` specifies receive or transmit
      - ``bits`` specifies sample size (bits), 16 or 32
      - ``format`` specifies channel format, STEREO or MONO