Geometry Shader Support For RadeonSI's NIR Back-End

AMD this year has been developing a NIR back-end for the RadeonSI Gallium3D driver in part for supporting the ARB_gl_spirv extension in being able to re-use/share some code with the RADV Vulkan driver that obviously already deals with SPIR-V and relies on NIR for its intermediate representation. Now support for geometry shaders is coming to RadeonSI NIR...