Hi~
Here already provided the information where the [imx8mp-rsb3720-a1-rpmsg.dts] file is.
EPC-3720 M7 Debug - Technical Supports / Software - Advantech AIM-Linux Community
For convenient to use, I have provided the imx8mp-rsb3720-a1-rpmsg.dts in this post. you can download it and copy to the kernel source and modify for your application.
Download from the link here: