pvr: New driver-compiler descriptor set approach
This is a step towards flushing out the driver-compiler interface.
- The allocation of shared regs is now done by the driver and an info struct with their layout is passed to the compiler.
- The compiler now uses the descriptors setup by the driver to access resources from memory.
To simplify and get things working quicker we decided to access all resources directly from main memory, as well as the descriptor set itself. Not great for performance but it should get more things working quicker since we avoid needing to add a whole lot of code (e.g. adding support for indexing a buffer resource from the shared regs, the compiler inspecting shaders to determine the size of the UBOs since that info is not passed to the driver directly, etc.) before getting anything else working.