Core: Make CPU_POWERDOWN the initial CPU state.

This isn't a correct state for the CPU to begin in when starting the application.

Also CPU_STEPPING as an initial state causes the emulator to crash if you use any of the debugger stepping buttons, since it checks if the CPU is in the CPU_STEPPING state before performing their functions.

Source/Core/Core/PowerPC/PowerPC.cpp

@@ -30,7 +30,7 @@ namespace PowerPC
 
 // STATE_TO_SAVE
 PowerPCState GC_ALIGNED16(ppcState);
-static volatile CPUState state = CPU_STEPPING;
+static volatile CPUState state = CPU_POWERDOWN;
 
 Interpreter * const interpreter = Interpreter::getInstance();
 static CoreMode mode;