dm: core: Add function to access uclass priv

Add functions so this information is not accessed directly. This will be
needed for of-platdata which stores it in a different place.

Signed-off-by: Simon Glass <sjg@chromium.org>

include/dm/uclass.h

@@ -114,6 +114,14 @@ struct uclass_driver {
 #define UCLASS_DRIVER(__name)						\
 	ll_entry_declare(struct uclass_driver, __name, uclass_driver)
 
+/**
+ * uclass_get_priv() - Get the private data for a uclass
+ *
+ * @uc		Uclass to check
+ * @return private data, or NULL if none
+ */
+void *uclass_get_priv(const struct uclass *uc);
+
 /**
  * uclass_get() - Get a uclass based on an ID, creating it if needed
  *