ramips: add support for TP-Link TL-WR841n v14

ramips: add support for TP-Link TL-WR841n v14

TP-Link TL-WR841n v14 is a router based on MediaTek MT7628N.

- MediaTek MT7628NN
- 32 MB of RAM
- 4 MB of FLASH
- 2T2R 2.4 GHz
- 5x 10/100 Mbps Ethernet

Installation:
- copy the
  'openwrt-ramips-mt76x8-tl-wr841n-v14-squashfs-tftp-recovery.bin'
  file to your tftp server root and rename it to 'tp_recovery.bin'.
- configure your PC running the TFTP server with the static IP address
  192.168.0.66/24
- push the reset button and plug in the power connector. Wait until
  the orange led starts blinking (~6sec)

Signed-off-by: Alexander Müller <donothingloop@gmail.com>
Signed-off-by: Alexander Couzens <lynxis@fe80.eu> [small modifications gpio-hog]