### etnaviv_noop backend

This implements the minimum of etnaviv in order to make shader-db work.
The submit ioctl is stubbed out to not execute anything.

Export `MESA_LOADER_DRIVER_OVERRIDE=etnaviv
LD_PRELOAD=$prefix/lib/libetnaviv_noop_drm_shim.so`.

It is possible to select a specific GPU model by setting the ETNA_SHIM_GPU
environment variable.

The following GPU models are available:
- GC2000 (default)
- GC3000
- GC7000L