ath79: add support for D-Link DIR-629 A1

ath79: add support for D-Link DIR-629 A1

Specifications:
  SOC:      QCA9588 CPU 720 MHz AHB 200 MHz
  Switch:   AR8236
  RAM:      64 MiB DDR2-600
  Flash:    8 MiB
  WLAN:     Wi-Fi4 2.4 GHz 3*3
  LAN:      LAN ports *4
  WAN:      WAN port *1
  Buttons:  reset *1 + wps *1
  LEDs: ethernet *5, power, wlan, wps

MAC Address:
  use      address               source
  label    70:62:b8:xx:xx:96     lan && wlan
  lan      70:62:b8:xx:xx:96     mfcdata@0x35
  wan      70:62:b8:xx:xx:97     mfcdata@0x6a
  wlan     70:62:b8:xx:xx:96     mfcdata@0x51

Install via Web UI:
  Apply factory image in the stock firmware's Web UI.

Install via Emergency Room Mode:
  DIR-629 A1 will enter recovery mode when the system fails to boot or
  press reset button for about 10 seconds.

  First, set IP address to 192.168.0.1 and server IP to 192.168.0.10.
  Then we can open http://192.168.0.1 in the web browser to upload
  OpenWrt factory image or stock firmware. Some modern browsers may
  need to turn on compatibility mode.

Signed-off-by: Shiji Yang <yangshiji66@qq.com>