trace: Add event "guest_cpu_enter"

Signals the hot-plugging of a new virtual (guest) CPU.

Signed-off-by: Lluís Vilanova <vilanova@ac.upc.edu>
Message-id: 147428971313.15111.18023030883528426840.stgit@fimbulvetr.bsc.es
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

trace/control-target.c

@@ -9,6 +9,7 @@
 
 #include "qemu/osdep.h"
 #include "cpu.h"
+#include "trace.h"
 #include "trace/control.h"
 #include "translate-all.h"
 
@@ -117,4 +118,6 @@ void trace_init_vcpu(CPUState *vcpu)
             }
         }
     }
+
+    trace_guest_cpu_enter(vcpu);
 }