hw/drivers/i2s: Fix build for MCUs that don't have fewer I2S
hw/drivers/i2s: Fix build for MCUs that don't have fewer I2S

I2S number can very from MCU to MCU.
I2S2 and I2S3 are common but not many MCUs have 5 I2S blocks.

This adds proper preprocessor guards against non existing configurations.

mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core