firmware: scmi: support dummy channels for sandbox agent

In sandbox scmi agent, channels are not used at all. But in this patch,
dummy channels are supported in order to test protocol-specific channels.

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Etienne Carriere <etienne.carriere@foss.st.com>
diff --git a/arch/sandbox/include/asm/scmi_test.h b/arch/sandbox/include/asm/scmi_test.h
index c72ec1e..75cb462 100644
--- a/arch/sandbox/include/asm/scmi_test.h
+++ b/arch/sandbox/include/asm/scmi_test.h
@@ -89,6 +89,14 @@
 
 #ifdef CONFIG_SCMI_FIRMWARE
 /**
+ * sandbox_scmi_channel_id - Get the channel id
+ * @dev:	Reference to the SCMI protocol device
+ *
+ * Return:	Channel id
+ */
+unsigned int sandbox_scmi_channel_id(struct udevice *dev);
+
+/**
  * sandbox_scmi_service_ctx - Get the simulated SCMI services context
  * @return:	Reference to backend simulated resources state
  */
@@ -101,6 +109,11 @@
  */
 struct sandbox_scmi_devices *sandbox_scmi_devices_ctx(struct udevice *dev);
 #else
+inline unsigned int sandbox_scmi_channel_id(struct udevice *dev);
+{
+	return 0;
+}
+
 static inline struct sandbox_scmi_service *sandbox_scmi_service_ctx(void)
 {
 	return NULL;