intel/rt: Implement support for shader call payloads

Both traceRay() and executeCallable() take a payload parameter which
gets passed from the caller to the callee and which the callee can write
to pass data back to the caller.  We implement these by passing a
pointer to the data structure in the callee to the caller as the second
QWord on its stack.  Coming out of spirv_to_nir, the incoming call
payloads get the nir_var_shader_call_data variable mode allowing us to
easily identify them.  Outgoing call payloads get assigned the
nir_var_shader_temp mode and will have been turned into function_temp by
nir_lower_global_vars_to_local.  All we have to do is crawl the shader
looking for references to the nir_var_shader_call_data variable and
rewrite those to use the passed in pointer.  nir_lower_explicit_io will
do the rest for us.

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

@@ -41,9 +41,10 @@ void brw_nir_lower_combined_intersection_any_hit(nir_shader *intersection,
                                                  const nir_shader *any_hit,
                                                  const struct gen_device_info *devinfo);
 
-/* We reserve the first 8B of the stack for callee data pointers */
+/* We reserve the first 16B of the stack for callee data pointers */
 #define BRW_BTD_STACK_RESUME_BSR_ADDR_OFFSET 0
-#define BRW_BTD_STACK_CALLEE_DATA_SIZE 8
+#define BRW_BTD_STACK_CALL_DATA_PTR_OFFSET 8
+#define BRW_BTD_STACK_CALLEE_DATA_SIZE 16
 
 /* We require the stack to be 8B aligned at the start of a shader */
 #define BRW_BTD_STACK_ALIGN 8