dm: migrate the dm_warn to use the log macro

Migrate the dm_warn function to log macro with
LOGC_DM category and LOGL_WARNING level.

This macro allows filtering with log command and allows
output on all log backend.

Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/include/dm/util.h b/include/dm/util.h
index 138893c..c634e47 100644
--- a/include/dm/util.h
+++ b/include/dm/util.h
@@ -7,7 +7,7 @@
 #define __DM_UTIL_H
 
 #if CONFIG_IS_ENABLED(DM_WARN)
-void dm_warn(const char *fmt, ...);
+#define dm_warn(fmt...) log(LOGC_DM, LOGL_WARNING, ##fmt)
 #else
 static inline void dm_warn(const char *fmt, ...)
 {