Seems like the document you linked to (and others like it for different cores) do not mention the C header file(s) that my application must #include. What is it? And do you have any example/demo code to build with Yocto that uses the VPU API?
In the latest BSP documentation, there is a PDF file i.MX_VPU_Application_Programming_Interface_Linux_Reference_Manual.pdf. You can take this for reference.