thunderbolt: Make usb4_switch_map_usb3_down() also return enabled ports

We need to call this on enabled ports in order to find the mapping from
host router USB4 port to a USB 3.x downstream adapter, so make the
function return enabled ports as well.

While there fix parameter alignment in tb_find_usb3_down().

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>