[mips/onionomega] WiFi & gpio kernel configuration bits

This patch adds missing hints for ath0 (eepromaddr) and GPIO (mask & leds).
ath0 doesn't work without eeprom hints, so this commit should make wifi
works on Onion Omega.

GPIO mask is required if you want to use gpiobus and GPIO pins on your
board. Onion Omega has several leds connected to gpio pins (one on board,
one color on dock).
This commit adds mask for gpiobus and allow you to turn off/on leds via
/dev/leds/{board,blue,green,red} (on by default).

Tested on Onion Omega 1.

Reviewed by: adrian
Approved by: adrian (mentor)
Differential Revision: https://reviews.freebsd.org/D9107