test/py: Add an extlinux file similar to Ubuntu

Add an extlinux configuration-file that contains a few entries as
created by the u-boot-menu package in Ubuntu 24.04

Increase the number of sandbox-USB-hub ports to permit this.

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

drivers/usb/emul/sandbox_hub.c

@@ -10,7 +10,7 @@
 #include <dm/device-internal.h>
 
 /* We only support up to 8 */
-#define SANDBOX_NUM_PORTS	4
+#define SANDBOX_NUM_PORTS	8
 
 struct sandbox_hub_plat {
 	struct usb_dev_plat plat;