RADV: Add dual level cache support to reduce cache size on Vulkan drivers

Note: When running https://gitlab.freedesktop.org/pendingchaos/radv_fossils the run sometimes fails hence the WIP. I'm still trying to track down if this is due to some kind of the threading problem or something else.

These will be used to implement a dual layer cache allowing us to avoid duplicate shaders within different pipelines in Vulkan drivers.

Currently we only enable this for the single file cache type.