kernel/thread: Include thread-related enums within the kernel namespace

Previously, these were sitting outside of the Kernel namespace, which
doesn't really make sense, given they're related to the Thread class
which is within the Kernel namespace.

src/core/hle/service/nwm/nwm_uds.cpp

@@ -1162,7 +1162,7 @@ void NWM_UDS::ConnectToNetwork(Kernel::HLERequestContext& ctx) {
     connection_event = ctx.SleepClientThread(
         Kernel::GetCurrentThread(), "uds::ConnectToNetwork", UDSConnectionTimeout,
         [](Kernel::SharedPtr<Kernel::Thread> thread, Kernel::HLERequestContext& ctx,
-           ThreadWakeupReason reason) {
+           Kernel::ThreadWakeupReason reason) {
             // TODO(B3N30): Add error handling for host full and timeout
             IPC::RequestBuilder rb(ctx, 0x1E, 1, 0);
             rb.Push(RESULT_SUCCESS);