etnaviv: add disk cache

Adds a shader disk-cache for shader variants.  Note that builds with
`-Dshader-cache=false` have no-op stubs with `disk_cache_create()` that
returns NULL.

This shader disk-cache gets used when using NIR only. Helps to save
about 1-2 minutes for a deqp run on gc2000.

Signed-off-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6669>
10 files changed