usb: aspeed-vhub: support test mode feature

Support aspeed usb vhub set feature to test mode.

Signed-off-by: Neal Liu <neal_liu@aspeedtech.com>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Link: https://lore.kernel.org/r/20211208100545.1441397-5-neal_liu@aspeedtech.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>