bootstd: Add a system bootdev for strange boot methods

Some boot methods don't act on a single bootdev but instead do their own
thing. An example is EFI bootmgr which scan various devices using its own
logic. Add a bootdev to handle this.

Signed-off-by: Simon Glass <sjg@chromium.org>

boot/bootstd-uclass.c

@@ -150,6 +150,12 @@ int dm_scan_other(bool pre_reloc_only)
 		}
 	}
 
+	/* Create the system bootdev too */
+	ret = device_bind_driver(bootstd, "system_bootdev", "system-bootdev",
+				 &dev);
+	if (ret)
+		return log_msg_ret("sys", ret);
+
 	return 0;
 }