There is no ready to use software mechanism to control the VPU load/usage. You can use the VPU API to check the VPU ready/busy status to calculate its usage. For more information, please refer to the VPU API User Manual document, included in the Linux BSP documentation bundle.
Also, you can make some estimations on the VPU load related to the maximum VPU processing capability numbers. The maximum VPU performance allows it to encode or decode one Full HD (1920x180) at 30fps video stream at a time.