dde_linux: initialize wait_bit subsystem

This is needed to compile kernel/sched/wait_bit.c needed by
x86 SMP as prerequisite for kernel/softirq.c.

Ref genodelabs/genode#4562

repos/dde_linux/src/app/wireguard/dummies.c

@@ -283,3 +283,10 @@ __wsum csum_partial(const void * buff,int len,__wsum sum)
 {
 	lx_emul_trace_and_stop(__func__);
 }
+
+
+#include <linux//wait_bit.h>
+void __init wait_bit_init(void)
+{
+	lx_emul_trace(__func__);
+}

repos/dde_linux/src/lib/lx_emul/start.c

@@ -107,6 +107,7 @@ int lx_emul_init_task_function(void * dtb)
 
 	jump_label_init();
 	kmem_cache_init();
+	wait_bit_init();
 	radix_tree_init();
 	workqueue_init_early();