usb: of: add functions to bind a companion controller

EHCI controllers will have a companion controller. However, on platform
bus, there was difficult to bind them in previous code. So, this
patch adds helper functions to bind them using a "companion" property.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/include/linux/usb/of.h b/include/linux/usb/of.h
index 5ff9032..4031f47 100644
--- a/include/linux/usb/of.h
+++ b/include/linux/usb/of.h
@@ -18,6 +18,7 @@ int of_usb_update_otg_caps(struct device_node *np,
 			struct usb_otg_caps *otg_caps);
 struct device_node *usb_of_get_child_node(struct device_node *parent,
 			int portnum);
+struct device *usb_of_get_companion_dev(struct device *dev);
 #else
 static inline enum usb_dr_mode
 of_usb_get_dr_mode_by_phy(struct device_node *np, int arg0)
@@ -38,6 +39,10 @@ static inline struct device_node *usb_of_get_child_node
 {
 	return NULL;
 }
+static inline struct device *usb_of_get_companion_dev(struct device *dev)
+{
+	return NULL;
+}
 #endif
 
 #if IS_ENABLED(CONFIG_OF) && IS_ENABLED(CONFIG_USB_SUPPORT)