scx: Validate that cpu callbacks can be sleepable

Now that ops.cpu_online() and ops.cpu_offline() can be sleepable,
let's update their test BPF progs to be sleepable to validate.

Signed-off-by: David Vernet <void@manifault.com>

tools/testing/selftests/sched_ext/hotplug.bpf.c

@@ -28,12 +28,12 @@ static void exit_from_hotplug(s32 cpu, bool onlining)
 		     onlining ? "online" : "offline");
 }
 
-void BPF_STRUCT_OPS(hotplug_cpu_online, s32 cpu)
+void BPF_STRUCT_OPS_SLEEPABLE(hotplug_cpu_online, s32 cpu)
 {
 	exit_from_hotplug(cpu, true);
 }
 
-void BPF_STRUCT_OPS(hotplug_cpu_offline, s32 cpu)
+void BPF_STRUCT_OPS_SLEEPABLE(hotplug_cpu_offline, s32 cpu)
 {
 	exit_from_hotplug(cpu, false);
 }