In I2C slave mode, clock source can now be changed, according to
the flags specified in `i2c_config_t` structure. Thus, ESP32-S2
can now act as an I2C slave, even with a 400KHz master clock.
Only a single command will be allocated now when a read or write is
prepared in the command list. The size of a command's buffer is not
limited to 255 bytes anymore.