ramips: add support for D-Link DAP-1620 B1

The DAP-1620 rev B is a wall-plug AC1300 repeater.

Specifications:
- MT7621AT, 256 MiB RAM, 16 MiB SPI NOR
- MT7615DN 2x2 802.11n +2x2 802.11ac (DBDC)
- Ethernet: 1 port 10/100/1000
- Status LEDs (1x red+green)
- LED RSSI bargraph (2x green, 1x red+green)

Installation:
- Keep reset button pressed during plug-in
- Web Recovery Updater is at 192.168.0.50
- Upload factory.bin, confirm flashing
  (seems to work best with Chromium-based browsers)

Revert to OEM firmware:
- tail -c+117 DAP1620B1_FW212B03.bin | \
  openssl aes-256-cbc -d -md md5 -out decrypted.bin \
  -k 905503a4e0c3cd3c1ce062246de427a68962347e
- flash decrypted.bin via D-Link Web Recovery

Signed-off-by: Rani Hod <rani.hod@gmail.com>

target/linux/ramips/mt7621/base-files/etc/board.d/01_leds

@@ -60,6 +60,13 @@ jcg,y2|\
 xzwifi,creativebox-v1)
 	ucidef_set_led_netdev "internet" "internet" "blue:internet" "wan"
 	;;
+dlink,dap-1620-b1)
+	ucidef_set_rssimon "wlan1" "200000" "1"
+	ucidef_set_led_rssi "rssilow" "RSSILOW" "red:rssilow" "wlan1" "1" "40"
+	ucidef_set_led_rssi "rssimediumlow" "RSSIMEDIUMLOW" "green:rssilow" "wlan1" "21" "100"
+	ucidef_set_led_rssi "rssimediumhigh" "RSSIMEDIUMHIGH" "green:rssimed" "wlan1" "61" "100"
+	ucidef_set_led_rssi "rssihigh" "RSSIHIGH" "green:rssihigh" "wlan1" "81" "100"
+	;;
 dlink,dap-x1860-a1)
 	ucidef_set_rssimon "wlan1" "200000" "1"
 	ucidef_set_led_rssi "rssilow" "RSSILOW" "orange:rssilow" "wlan1" "1" "25"

target/linux/ramips/mt7621/base-files/etc/board.d/02_network

@@ -14,6 +14,7 @@ ramips_setup_interfaces()
 	ampedwireless,ally-00x19k|\
 	asus,rp-ac56|\
 	asus,rp-ac87|\
+	dlink,dap-1620-b1|\
 	dlink,dap-x1860-a1|\
 	edimax,re23s|\
 	mikrotik,ltap-2hnd|\