dm: core: Add a function to look up a uclass by name

Each uclass has a driver name which we can use to look up the uclass. This
is useful for logging, where the uclass ID is used as the category.

Add a function to handle this, as well as a test.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/include/dm/uclass.h b/include/dm/uclass.h
index 709f661..3a01abc 100644
--- a/include/dm/uclass.h
+++ b/include/dm/uclass.h
@@ -128,6 +128,14 @@
 const char *uclass_get_name(enum uclass_id id);
 
 /**
+ * uclass_get_by_name() - Look up a uclass by its driver name
+ *
+ * @name: Name to look up
+ * @returns the associated uclass ID, or UCLASS_INVALID if not found
+ */
+enum uclass_id uclass_get_by_name(const char *name);
+
+/**
  * uclass_get_device() - Get a uclass device based on an ID and index
  *
  * The device is probed to activate it ready for use.