ARM: move kernel func event to correct location.

With the recent series of patches, the symbol table loading moved from
"construct" time to "init" time, but the kernel function event
callback registration was left behind. This patch moves it to the
proper location.

src/arch/arm/system.cc

@@ -55,7 +55,6 @@ using namespace Linux;
 ArmSystem::ArmSystem(Params *p)
     : System(p), bootldr(NULL)
 {
-    debugPrintkEvent = addKernelFuncEvent<DebugPrintkEvent>("dprintk");
 }
 
 void
@@ -113,6 +112,7 @@ ArmSystem::initState()
         }
     }
 
+    debugPrintkEvent = addKernelFuncEvent<DebugPrintkEvent>("dprintk");
 }
 
 ArmSystem::~ArmSystem()