(Buildroot) How to load modules automatically

I'd like to load some additional modules at boot.

This works fine from the command line:

modprobe -a i2c-devmodprobe -a snd-soc-pcm512xmodprobe -a snd-soc-wm8804

But I want this done at boot. I've tried creating /etc/modules, /etc/modprobe.conf and /etc/modprobe.d/i2c-dev.conf, etc. with the module name in there, but no luck.

I'm using a buildroot-2017-08, which I believes uses kmod, with a BusyBox init.

I can just create an init.d script, but I think there's a specific location that should contain the list of modules to load.