I2S library: Support for 24 Bit samples

I tried to hook up an PCM1808 ADC to an Arduino MKR Zero using this library. After it failed to initialize I2S many times and I wondered why, I looked at the source code and discovered that 24 Bit sample width is not supported by the library. Please implement support for this.

Start by locating the I2S library source and its sample-width initialization and handling, then trace the failure reported with the Arduino MKR Zero and PCM1808 ADC. Done means the library accepts 24-bit samples and initializes successfully for that use case; the issue does not name a specific file or test.

Written by the indexing model from the issue text.