ARM: dts: BCM5301X: Specify USB ports for USB LED of Luxul XWR-1200

This info can be used by operating system to setup LED behavior.

Reported-by: Dan Haab <dhaab@luxul.com>
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>