REORG: thread/sched: move the last dynamic thread_info to thread_ctx

The last 3 fields were 3 list heads that are per-thread, and which are:
  - the pool's LRU head
  - the buffer_wq
  - the streams list head

Moving them into thread_ctx completes the removal of dynamic elements
from the struct thread_info. Now all these dynamic elements are packed
together at a single place for a thread.
diff --git a/src/flt_spoe.c b/src/flt_spoe.c
index 3262fd0..3f17bcb 100644
--- a/src/flt_spoe.c
+++ b/src/flt_spoe.c
@@ -2867,7 +2867,7 @@
 	if (b_alloc(buf))
 		return 1;
 
-	LIST_APPEND(&ti->buffer_wq, &buffer_wait->list);
+	LIST_APPEND(&th_ctx->buffer_wq, &buffer_wait->list);
 	return 0;
 }