ar71xx: Add support for TP-Link CPE210 v3

ar71xx: Add support for TP-Link CPE210 v3

Looks identical to the v2.

This PR adds support for a popular low-cost 2.4GHz N based AP

Specifications:
 - SoC: Qualcomm Atheros QCA9533 (650MHz)
 - RAM: 64MB
 - Storage: 8 MB SPI NOR
 - Wireless: 2.4GHz N based built into SoC 2x2
 - Ethernet: 1x 100/10 Mbps, integrated into SoC, 24V POE IN

Installation:
Flash factory image through stock firmware WEB UI
or through TFTP
To get to TFTP recovery just hold reset button while powering on for
around 4-5 seconds and release.
Rename factory image to recovery.bin
Stock TFTP server IP:192.168.0.100
Stock device TFTP adress:192.168.0.254

Tested-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
Signed-off-by: Robert Marko <robimarko@gmail.com>
[Rebased, adjusted for separate tplink-safeloader entry, dynamic partitioning]
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>