In multithreadead, load the game async.

This way if it takes time to load, things aren't frozen while it's doing
that.  This allows us to show any sort of loading animation or etc. we
want.

Before, it might show a odd looking game select screen while loading, and
then finally go to black.  Now it immediately goes to black.

Fixes #2030.

Core/System.cpp

@@ -301,8 +301,13 @@ void System_Wake() {
 }
 
 static bool pspIsInited = false;
+static bool pspIsIniting = false;
+
+bool PSP_InitStart(const CoreParameter &coreParam, std::string *error_string) {
+	if (pspIsIniting) {
+		return false;
+	}
 
-bool PSP_Init(const CoreParameter &coreParam, std::string *error_string) {
 #if defined(_WIN32) && defined(_M_X64)
 	INFO_LOG(BOOT, "PPSSPP %s Windows 64 bit", PPSSPP_GIT_VERSION);
 #elif defined(_WIN32) && !defined(_M_X64)
@@ -312,17 +317,30 @@ bool PSP_Init(const CoreParameter &coreParam, std::string *error_string) {
 #endif
 	coreParameter = coreParam;
 	coreParameter.errorString = "";
+	pspIsIniting = true;
 
 	if (g_Config.bSeparateCPUThread) {
 		Core_ListenShutdown(System_Wake);
 		CPU_SetState(CPU_THREAD_PENDING);
 		cpuThread = new std::thread(&CPU_RunLoop);
 		cpuThread->detach();
-		CPU_WaitStatus(cpuThreadReplyCond, &CPU_IsReady);
 	} else {
 		CPU_Init();
 	}
 
+	*error_string = coreParameter.errorString;
+	return coreParameter.fileToStart != "";
+}
+
+bool PSP_InitUpdate(std::string *error_string) {
+	if (pspIsInited || !pspIsIniting) {
+		return true;
+	}
+
+	if (g_Config.bSeparateCPUThread && !CPU_IsReady()) {
+		return false;
+	}
+
 	bool success = coreParameter.fileToStart != "";
 	*error_string = coreParameter.errorString;
 	if (success) {
@@ -333,7 +351,22 @@ bool PSP_Init(const CoreParameter &coreParam, std::string *error_string) {
 		}
 	}
 	pspIsInited = success;
-	return success;
+	pspIsIniting = false;
+	return true;
+}
+
+bool PSP_Init(const CoreParameter &coreParam, std::string *error_string) {
+	PSP_InitStart(coreParam, error_string);
+
+	if (g_Config.bSeparateCPUThread) {
+		CPU_WaitStatus(cpuThreadReplyCond, &CPU_IsReady);
+	}
+
+	return PSP_InitUpdate(error_string);
+}
+
+bool PSP_IsIniting() {
+	return pspIsIniting;
 }
 
 bool PSP_IsInited() {
@@ -362,6 +395,7 @@ void PSP_Shutdown() {
 	host->SetWindowTitle(0);
 	currentMIPS = 0;
 	pspIsInited = false;
+	pspIsIniting = false;
 }
 
 void PSP_RunLoopUntil(u64 globalticks) {