ath79: add support for Telco T1

ath79: add support for Telco T1

Description:
    2x 100Mbps Etherent ports
    24V passive PoE
    64MB RAM
    16MB Flash
    2.4GHz WiFi
    1x WiFi antenna (RP-SMA connector)
    1x LTE antenna (SMA connector)
    Sierra Wireless MC7430 LTE modem

Flash instructions:
    Original firmware is based on OpenWrt.
    Flash using sysupgrade -n

SUPPORTED_DEVICES is added to support factory firmware.

Signed-off-by: Nicholas Smith <nicholas.smith@telcoantennas.com.au>
[add missing led_rssi0 DT label, add SUPPORTED_DEVICES]
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>