Kernel/HLE: Use a mutex to synchronize access to the HLE kernel state between the cpu thread and any other possible threads that might touch the kernel (network thread, etc).

This mutex is acquired in SVC::CallSVC, ie, as soon as the guest application enters the HLE kernel, and should be acquired by the aforementioned threads before modifying kernel structures.

src/core/hle/kernel/kernel.h

@@ -129,4 +129,4 @@ void Init(u32 system_mode);
 /// Shutdown the kernel
 void Shutdown();
 
-} // namespace
+} // namespace Kernel