Add I2S_MCLK support

[wschuma]

Original behavior is untouched (I2S_MCLK disabled). Just add #define I2S_MCLK 0 in myoptions.h if needed.

Requires a board where GPIO 0 is available.

[amstereo4ever]

Hi there,
yes adding MCLK officially would be very much appreciated. I use it for a CS4344 DAC and at the same time a Wolfson WM8804 to output S/PDIF and analog at the same time. As a third output I am going to use a QN8007 I2S to FM modulator. So adding MCLK would open a lot of added functionality. It would be great if it could find its way into an upcoming release.

[amstereo4ever]

Extra info, I am using an ESP32 S3 N16R8 the MCLK is output on GPIO4. As Wolle had commented in his audio library that on ESP32 regular you have to use GPIO 0 but with ESP32 S3 any GPIO will work. I have not been able to get the MCLK to work on an older ESP32 using GPIO 0 but with the ESP32 S3 it worked right away.