dm: core: Add a few more specific child-finding functions

Add two functions which can find a child device by uclass or by name.
The first is useful with Multi-Function-Devices (MFDs) to find one of a
particular type. The second is useful when only the name is known.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/core/device.c b/drivers/core/device.c
index 47a697f..836bcad 100644
--- a/drivers/core/device.c
+++ b/drivers/core/device.c
@@ -699,6 +699,40 @@
 	return -ENODEV;
 }
 
+int device_find_first_child_by_uclass(struct udevice *parent,
+				      enum uclass_id uclass_id,
+				      struct udevice **devp)
+{
+	struct udevice *dev;
+
+	*devp = NULL;
+	list_for_each_entry(dev, &parent->child_head, sibling_node) {
+		if (device_get_uclass_id(dev) == uclass_id) {
+			*devp = dev;
+			return 0;
+		}
+	}
+
+	return -ENODEV;
+}
+
+int device_find_child_by_name(struct udevice *parent, const char *name,
+			      struct udevice **devp)
+{
+	struct udevice *dev;
+
+	*devp = NULL;
+
+	list_for_each_entry(dev, &parent->child_head, sibling_node) {
+		if (!strcmp(dev->name, name)) {
+			*devp = dev;
+			return 0;
+		}
+	}
+
+	return -ENODEV;
+}
+
 struct udevice *dev_get_parent(const struct udevice *child)
 {
 	return child->parent;