turnip,freedreno: Support extra descriptor sets on A7XX

This MR changes the amount of descriptor sets from being fixed at compile-time into a per-GPU property to accommodate 7 usable descriptor sets on A7XX compared to 4 on A6XX with one internally reserved. As a part of this, the descriptor being reserved for descriptor set dynamic offsets support can be optionally disabled via the driconf option tu_dont_reserve_descriptor_set which will trade-off support for dynamic offsets in exchange for an extra usable descriptor set.

This is particularly handy on A6XX where it frees 5 usable descriptor sets with certain engines such as Source 2 require while seemingly not using dynamic offsets. It should similarly work on A7XX to free up 8 usable descriptor sets but it's unlikely to be a requirement in practice.