hle: Get rid of global access to g_reschedule

This shouldn't be directly exposed if there's already a partial API that operates on it.
We can just provide the rest of that API.

src/core/hle/hle.h

@@ -13,9 +13,9 @@ const Handle INVALID_HANDLE = 0;
 
 namespace HLE {
 
-extern bool g_reschedule;   ///< If true, immediately reschedules the CPU to a new thread
-
 void Reschedule(const char *reason);
+bool RescheduleIsPending();
+void DoneRescheduling();
 
 void Init();
 void Shutdown();