I noticed that the kernel usb audio driver is not enabled on m3ulcb boards, however some BSPs have it on in their layers (like dra7xx-evm where I had been using that driver). Also, the renesas gen2 bsp bbappend has a usbaudio.cfg fragment that's unused by the recipe (though present). Fix this by moving the usbaudio.cfg fragment to linux-agl.inc so it's picked up by all kernel builds.