core_timing: Namespace all functions and constants in core_timing's header

All of these variables and functions are related to timings and should be within the namespace.

src/core/hle/kernel/thread.cpp

@@ -146,7 +146,8 @@ void Thread::WakeAfterDelay(s64 nanoseconds) {
     if (nanoseconds == -1)
         return;
 
-    CoreTiming::ScheduleEvent(nsToCycles(nanoseconds), ThreadWakeupEventType, callback_handle);
+    CoreTiming::ScheduleEvent(CoreTiming::nsToCycles(nanoseconds), ThreadWakeupEventType,
+                              callback_handle);
 }
 
 void Thread::CancelWakeupTimer() {