core: reset kernel after service manager in Shutdown

Services can hold kernel objects and do cleanup upon destruction, so we need to keep the kernel alive longer. The new order approximnately resembles the reverse construction order. I will revisit the ordering issue and make it less error-prone after global state cleanup

src/core/core.cpp

@@ -291,7 +291,6 @@ void System::Shutdown() {
     // Shutdown emulation session
     GDBStub::Shutdown();
     VideoCore::Shutdown();
-    kernel.reset();
     HW::Shutdown();
     telemetry_session.reset();
     rpc_server.reset();
@@ -299,6 +298,7 @@ void System::Shutdown() {
     service_manager.reset();
     dsp_core.reset();
     cpu_core.reset();
+    kernel.reset();
     timing.reset();
     app_loader.reset();