Hi @bretts
My apologies for the delayed response.
To add custom driver, the simplest way is to edit the Cmakelist associated to your project.

This way, I created the most simple driver on the drivers folder.

Then I called the driver function on main and it worked. This is related to this.
I think it is okay for a single file, but for a complete directory not. So I think this could do better the job
If you want to include an nxp sdk driver , you could check out this post from Derek
https://community.nxp.com/t5/Zephyr-Project-Knowledge-Base/Using-MCUXpresso-SDK-drivers-in-a-Zephyr-...
I hope this could help you!
Diego