timer: introduce new QEMU_CLOCK_VIRTUAL_RT clock

This patch introduces new QEMU_CLOCK_VIRTUAL_RT clock, which
should be used for icount warping.  In the next patch, it
will be used to avoid a huge icount warp when a virtual
machine is stopped for a long time.

Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

qemu-timer.c

@@ -566,6 +566,8 @@ int64_t qemu_clock_get_ns(QEMUClockType type)
             notifier_list_notify(&clock->reset_notifiers, &now);
         }
         return now;
+    case QEMU_CLOCK_VIRTUAL_RT:
+        return cpu_get_clock();
     }
 }