kernel: add package for usbport LED trigger

This is upstream alternative for LEDE's ledtrig-usbdev. It's main
advantages are:
1) Support for assigning more than 1 USB port to the LED
2) Setting proper state when activating with device already connected
3) FWIW it's an upstream driver

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>