scmi: define LOG_CATEGORY

Define LOG_CATEGORY to allow filtering with log command.

Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>
diff --git a/drivers/firmware/scmi/smccc_agent.c b/drivers/firmware/scmi/smccc_agent.c
index 81c2884..f185891 100644
--- a/drivers/firmware/scmi/smccc_agent.c
+++ b/drivers/firmware/scmi/smccc_agent.c
@@ -3,6 +3,8 @@
  * Copyright (C) 2020 Linaro Limited.
  */
 
+#define LOG_CATEGORY UCLASS_SCMI_AGENT
+
 #include <common.h>
 #include <dm.h>
 #include <errno.h>