This adds the gpio switch to enable PoE passthrough on Ubiquiti
Nanostation (XM/XW).
Values are copied from the implementation in ar71xx.
GPIO values checked on:
- NanoStation M5 XW
- NanoStation M2 XM
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
(cherry picked from commit 317e98a5a2c6f1e2ac599ec530478669b965602c)