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/kernel/thread.h

@@ -15,6 +15,12 @@
 #include "core/hle/kernel/wait_object.h"
 #include "core/hle/result.h"
 
+namespace Kernel {
+
+class KernelCore;
+class Process;
+class Scheduler;
+
 enum ThreadPriority : u32 {
     THREADPRIO_HIGHEST = 0,       ///< Highest thread priority
     THREADPRIO_USERLAND_MAX = 24, ///< Highest thread priority for userland apps
@@ -54,12 +60,6 @@ enum class ThreadWakeupReason {
     Timeout // The thread was woken up due to a wait timeout.
 };
 
-namespace Kernel {
-
-class KernelCore;
-class Process;
-class Scheduler;
-
 class Thread final : public WaitObject {
 public:
     /**