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/core.cpp

@@ -52,7 +52,7 @@ void RunLoop(int tight_loop) {
     }
 
     HW::Update();
-    if (HLE::g_reschedule) {
+    if (HLE::RescheduleIsPending()) {
         Kernel::Reschedule();
     }
 }