intel/rt: Add a helper to create the raygen trampoline shader

Unlike graphics and compute pipelines, Vulkan ray-tracing pipelines do
not have a single entrypoint.  Instead, the raygen shader is specified
as a one-element shader binding table in the vkCmdTraceRay call.  This
means that raygen shaders have to be bindless shaders just like any
other ray tracing shader.  To launch them, we have a tiny compute shader
that acts as a trampoline and sets up the hotzone and uses btd_spawn to
fire off the raygen shader.

Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7356>

src/intel/compiler/brw_nir_rt.h

@@ -64,6 +64,9 @@ void brw_nir_lower_intersection_shader(nir_shader *intersection,
                                        const struct gen_device_info *devinfo);
 
 nir_shader *
+brw_nir_create_raygen_trampoline(const struct brw_compiler *compiler,
+                                 void *mem_ctx);
+nir_shader *
 brw_nir_create_trivial_return_shader(const struct brw_compiler *compiler,
                                      void *mem_ctx);