NOTE you do NOT need Vivante kernel drivers to build the Etnaviv GPU driver. You need the etnaviv DRM driver for that, which has been upstreamed and is part of Linux mainline.
This collection of kernel drivers is provided for historical purposes only. They are outdated and probably buggy.
If you are looking for recent stand-alone Vivante kernel drivers see https://github.com/Freescale/kernel-module-imx-gpu-viv .
If you have a device with Linux or Android with a Vivante GPU, your best bet is to find (or ask for) the GPL drivers for your specific device. At least you can be sure they work with your device.