Tegra/Nouveau Render-Only Gallium3D Support

With the Etnaviv driver bringing the Gallium3D "renderonly" library to Mesa Git, Alexandre Courbot of NVIDIA has sent out an updated patch for adding renderonly support to Tegra/Nouveau.

This patch was originally authored by Christian Gmeiner while the NVIDIA developer just ported it to the latest code-base and made some minor improvements. This 200+ lines of code allows for opening a Nouveau render device in order to transparent provide acceleration on Tegra.

The renderonly library adds support for render-only GPUs and was originally written for the Etnaviv/i.MX use-case. This library is a stop-gap measure until "GBM2" / a new memory allocation API to succeed GBM comes about.

This renderonly patch for Tegra/Nouveau can be found on Mesa-dev while waiting to see if it lands into Mesa Git within the next day for making it in the 17.0 release.