ramips: add support for TL-WA801ND v5

ramips: add support for TL-WA801ND v5

Specification:

- System-On-Chip: MediaTek MT7628NN
- CPU/Speed: 580 MHz
- Flash-Chip: ELM Technology GD25Q64
- Flash size: 8192 KiB
- RAM: 64 MiB
- Wireless No1: SoC-integrated: MT7628N 2.4GHz 802.11bgn

Currently the only method to install openwrt for the first time is via
TFTP recovery. After first install you can use regular updates.

Flash instructions:

1) To flash the recovery image, start a TFTP server with IP address
   192.168.0.66 and serve the recovery image named tp_recovery.bin.
2) Connect your device to the LAN port, then press the WPS and Reset
   button and power it up. Keep pressing the WPS/Reset button for
   10 seconds or until the lock LED is lighting up.
   It will try to download the recovery image and flash it.

It can take up to 2-3 minutes to finish. When it reaches 100%, the
router will reboot itself.

Signed-off-by: Romain MARIADASSOU <roms2000@free.fr>