This ports support for TP-Link TL-WR842N/ND v1 from ar71xx.

CPU: Atheros AR7241 400 MHz
RAM: 32 MiB
FLASH: 8 MiB
PORTS: 4 Port 100/10 Switch, 1 Port 100/10 Wan
WiFi: Atheros AR9287
LED: SYS, WiFi, LAN, WAN, 3G, QSS
BTN: WiFi, Reset/WPS

AR71xx target used "tl-mr3420" as board id so force flag is needed
if upgrading from old target.

Signed-off-by: Marcin Jurkowski <marcin1j@gmail.com>
Signed-off-by: Christian Lamparter <chunkeey@gmail.com> [trivial cleanup]