Defer HLE interrupts, vblank only when enabled.

Based on tests, vblank doesn't queue up (makes sense) while
interrupts are disabled.

I'm not 100% sure about the GPU stuff but it seems to only come
from HLE via sceGe, so this should fix those return values.

Core/HLE/sceDisplay.cpp

@@ -151,7 +151,7 @@ void hleEnterVblank(u64 userdata, int cyclesLate)
 	vblankWaitingThreads.clear();
 
 	// Trigger VBlank interrupt handlers.
-	__TriggerInterrupt(PSP_VBLANK_INTR);
+	__TriggerInterrupt(PSP_INTR_IMMEDIATE | PSP_INTR_ONLY_IF_ENABLED, PSP_VBLANK_INTR);
 
 	CoreTiming::ScheduleEvent(msToCycles(vblankMs) - cyclesLate, leaveVblankEvent, vbCount+1);