cpus: protect work list with work_mutex

Protect the list of queued work items with something other than
the BQL, as a preparation for running the work items outside it.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: KONRAD Frederic <fred.konrad@greensocs.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

qom/cpu.c

@@ -316,6 +316,7 @@ static void cpu_common_initfn(Object *obj)
 
     cpu->cpu_index = -1;
     cpu->gdb_num_regs = cpu->gdb_num_g_regs = cc->gdb_num_core_regs;
+    qemu_mutex_init(&cpu->work_mutex);
     QTAILQ_INIT(&cpu->breakpoints);
     QTAILQ_INIT(&cpu->watchpoints);
 }