dm: Add child_pre_probe() and child_post_remove() methods

Some devices (particularly bus devices) must track their children, knowing
when a new child is added so that it can be set up for communication on the
bus.

Add a child_pre_probe() method to provide this feature, and a corresponding
child_post_remove() method.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/include/dm/device.h b/include/dm/device.h
index 20207ce..c8a4072 100644
--- a/include/dm/device.h
+++ b/include/dm/device.h
@@ -118,6 +118,10 @@
  * @remove: Called to remove a device, i.e. de-activate it
  * @unbind: Called to unbind a device from its driver
  * @ofdata_to_platdata: Called before probe to decode device tree data
+ * @child_pre_probe: Called before a child device is probed. The device has
+ * memory allocated but it has not yet been probed.
+ * @child_post_remove: Called after a child device is removed. The device
+ * has memory allocated but its device_remove() method has been called.
  * @priv_auto_alloc_size: If non-zero this is the size of the private data
  * to be allocated in the device's ->priv pointer. If zero, then the driver
  * is responsible for allocating any data required.
@@ -143,6 +147,8 @@
 	int (*remove)(struct udevice *dev);
 	int (*unbind)(struct udevice *dev);
 	int (*ofdata_to_platdata)(struct udevice *dev);
+	int (*child_pre_probe)(struct udevice *dev);
+	int (*child_post_remove)(struct udevice *dev);
 	int priv_auto_alloc_size;
 	int platdata_auto_alloc_size;
 	int per_child_auto_alloc_size;