ath79: add support for Wallys DR531

Wallys DR531 is based on Qualcomm Atheros QCA9531 v2. Support for this
device was first introduced in e767980eb8 (ar71xx target).

Specifications:

- Qualcomm/Atheros QCA9531 v2
- 550/400/200 MHz (CPU/DDR/AHB)
- 2x 10/100 Mbps Ethernet
- 64 MB of RAM (DDR2)
- 8 MB of flash (SPI NOR)
- 2T2R 2.4 GHz Wi-Fi, with external PA (SE2576L), up to 30 dBm
- 2x MMCX connectors (optional IPEX/U.FL)
- mini PCIe connector (PCIe/USB buses and mini SIM slot)
- 7x LED, 1x button, 1x optional buzzer
- UART, JTAG and LED headers on PCB

Flash instruction (do it under U-Boot, using UART):

  tftpb 0x80060000 openwrt-ath79-...-dr531-squashfs-sysupgrade.bin
  erase 0x9f050000 +$filesize
  cp.b $fileaddr 0x9f050000 $filesize
  setenv bootcmd "bootm 0x9f050000"
  saveenv && reset

Signed-off-by: Piotr Dymacz <pepe2k@gmail.com>

target/linux/ath79/generic/base-files/etc/board.d/01_leds

@@ -356,6 +356,15 @@ ubnt,powerbeam-5ac-gen2)
 	ucidef_set_led_rssi "rssimediumhigh" "RSSIMEDIUMHIGH" "ubnt:blue:rssi2" "wlan0" "51" "100"
 	ucidef_set_led_rssi "rssihigh" "RSSIHIGH" "ubnt:blue:rssi3" "wlan0" "76" "100"
 	;;
+wallys,dr531)
+	ucidef_set_led_netdev "lan" "LAN" "$boardname:green:lan" "eth0"
+	ucidef_set_led_switch "wan" "WAN" "$boardname:green:wan" "switch0" "0x2"
+	ucidef_set_rssimon "wlan0" "200000" "1"
+	ucidef_set_led_rssi "sig1" "SIG1" "$boardname:green:sig1" "wlan0" "1" "100"
+	ucidef_set_led_rssi "sig2" "SIG2" "$boardname:green:sig2" "wlan0" "25" "100"
+	ucidef_set_led_rssi "sig3" "SIG3" "$boardname:green:sig3" "wlan0" "50" "100"
+	ucidef_set_led_rssi "sig4" "SIG4" "$boardname:green:sig4" "wlan0" "75" "100"
+	;;
 wd,mynet-wifi-rangeextender)
 	ucidef_set_led_netdev "lan" "LAN" "$boardname:green:lan" "eth0"
 	ucidef_set_rssimon "wlan0" "200000" "1"