dm: core: Export uclass_find_device_by_phandle()

This function may be useful to code outside of the code driver-model
implementation. Export it and add a test.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/core/uclass.c b/drivers/core/uclass.c
index d9c5719..9766aea 100644
--- a/drivers/core/uclass.c
+++ b/drivers/core/uclass.c
@@ -354,10 +354,8 @@
 }
 
 #if CONFIG_IS_ENABLED(OF_CONTROL)
-static int uclass_find_device_by_phandle(enum uclass_id id,
-					 struct udevice *parent,
-					 const char *name,
-					 struct udevice **devp)
+int uclass_find_device_by_phandle(enum uclass_id id, struct udevice *parent,
+				  const char *name, struct udevice **devp)
 {
 	struct udevice *dev;
 	struct uclass *uc;