v3dv/pipeline_cache: bare basic support for pipeline cache

v3dv/pipeline_cache: bare basic support for pipeline cache

And this means providing a proper cache object, and being able to
load/retrieve a cache data with a proper header. Not really caching
anything yet. That would be tackle on following patches.

Note that this no-op cache got all the specific pipeline_cache and
pipeline.cache tests passing on the rpi4.

The following tests are still crashing when using the simulator:
 dEQP-VK.synchronization.internally_synchronized_objects.pipeline_cache_compute
 dEQP-VK.synchronization.internally_synchronized_objects.pipeline_cache_graphics

But those are an issue of synchronization tests on the simulator, and
not related with the pipeline cache itself. In general synchronization
tests should be tested on the rpi4.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6766>