dm: core: Add a function to find any device from device tree

In some rare cases it is useful to be able to locate a device given a device
tree node offset. An example is when you have an alias that points to a node
and you want to find the associated device. The device may be SPI, MMC or
something else, but you don't need to know the uclass to find it.

Add a function to do a global search for a device, given its device tree
offset.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/include/dm/device.h b/include/dm/device.h
index 18296bb..9a94ee1 100644
--- a/include/dm/device.h
+++ b/include/dm/device.h
@@ -390,6 +390,20 @@
 				  struct udevice **devp);
 
 /**
+ * device_get_global_by_of_offset() - Get a device based on FDT offset
+ *
+ * Locates a device by its device tree offset, searching globally throughout
+ * the all driver model devices.
+ *
+ * The device is probed to activate it ready for use.
+ *
+ * @of_offset: Device tree offset to find
+ * @devp: Returns pointer to device if found, otherwise this is set to NULL
+ * @return 0 if OK, -ve on error
+ */
+int device_get_global_by_of_offset(int of_offset, struct udevice **devp);
+
+/**
  * device_find_first_child() - Find the first child of a device
  *
  * @parent: Parent device to search