test: dm: simplify SCMI unit test on sandbox

Adding SCMI base protocol makes it inconvenient to hold the agent instance
(udevice) locally since the agent device will be re-created per each test.
Just remove it and simplify the test flows.
The test scenario is not changed at all.

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 75cb462..ccb0df6 100644
--- a/arch/sandbox/include/asm/scmi_test.h
+++ b/arch/sandbox/include/asm/scmi_test.h
@@ -98,9 +98,11 @@
 
 /**
  * sandbox_scmi_service_ctx - Get the simulated SCMI services context
+ * sandbox_scmi_agent_ctx - Get the simulated SCMI agent context
+ * @dev:	Reference to the test agent
  * @return:	Reference to backend simulated resources state
  */
-struct sandbox_scmi_service *sandbox_scmi_service_ctx(void);
+struct sandbox_scmi_agent *sandbox_scmi_agent_ctx(struct udevice *dev);
 
 /**
  * sandbox_scmi_devices_ctx - Get references to devices accessed through SCMI
@@ -114,7 +116,7 @@
 	return 0;
 }
 
-static inline struct sandbox_scmi_service *sandbox_scmi_service_ctx(void)
+static struct sandbox_scmi_agent *sandbox_scmi_agent_ctx(struct udevice *dev)
 {
 	return NULL;
 }