I2S interface sample size configuration issue

The only sample size it is supporting is 32 bit right now.

Master/Slave | Transmit/Receive | Comments
-- | -- | --
Master | Transmit | Curie drives the I2S in 32 bit sample size only.
  |   | Have not found a Slave device that could not take 32 bit sample size.
Master | Receive | Could not find a transmitter that operates in Slave mode to test this combination.
Slave | Transmit | Could not find a receiver that operates in Master mode.
Slave | Receive | Curie works with variable sample size input.
  |   | Curie put the captured sample in 32 bit format with upper unused bits set to 0's.

Start by locating the I2S sample-size configuration and comparing behavior across the master/slave and transmit/receive combinations described in the issue. The issue does not specify the desired change or name files or tests; clarify the expected supported sample sizes and combinations before defining what done looks like.

Written by the indexing model from the issue text.