plugin: add qemu_plugin_outs helper

Having the plugins grab stdout and spew stuff there is a bit ugly and
certainly makes the tests look ugly. Provide a hook back into QEMU
which can be redirected as needed.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Aaron Lindsay <aaron@os.amperecomputing.com>

plugins/api.c

@@ -331,3 +331,11 @@ int qemu_plugin_n_max_vcpus(void)
     return get_ms()->smp.max_cpus;
 #endif
 }
+
+/*
+ * Plugin output
+ */
+void qemu_plugin_outs(const char *string)
+{
+    qemu_log_mask(CPU_LOG_PLUGIN, "%s", string);
+}

plugins/qemu-plugins.symbols

@@ -36,4 +36,5 @@
   qemu_plugin_vcpu_for_each;
   qemu_plugin_n_vcpus;
   qemu_plugin_n_max_vcpus;
+  qemu_plugin_outs;
 };