ath79: add support for TP-Link TL-WR940N v6

The TL-WR940N v6 is similar to v3/v4, it just has different
LEDs and MAC address assignment.

Specification:
- 750 MHz CPU
- 32 MB of RAM
- 4 MB of FLASH
- 2.4 GHz WiFi
- 4x 10/100 Mbps Ethernet

The use of LEDs is based on ar71xx, so blue LED is used for WAN
and orange LED for diag (boot/failsafe/etc.).

Flash instruction (WebUI):
Download *-factory.bin image and upload it via the firmwary upgrade
function of the stock firmware WebUI.

Flash instruction (TFTP):
1. Set PC to fixed ip address 192.168.0.66
2. Download *-factory.bin image and rename it to
   wr940nv6_tp_recovery.bin
3. Start a tftp server with the image file in its root directory
4. Turn off the router
5. Press and hold Reset button
6. Turn on router with the reset button pressed and wait ~15 seconds
7. Release the reset button and after a short time
the firmware should be transferred from the tftp server
8. Wait ~30 second to complete recovery.

Thanks to Manuel Kock for reviewing and testing this patch.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
Tested-by: Manuel Kock <github.web@manu.li>

target/linux/ath79/dts/tp9343_tplink_tl-wr940n-v6.dts

+// SPDX-License-Identifier: GPL-2.0-or-later OR MIT
+/dts-v1/;
+
+#include "tp9343_tplink_tl-wr94x.dtsi"
+
+/ {
+	compatible = "tplink,tl-wr940n-v6", "qca,tp9343";
+	model = "TP-Link TL-WR940N v6";
+
+	aliases {
+		led-boot = &led_diag_orange;
+		led-failsafe = &led_diag_orange;
+		led-running = &led_diag_orange;
+		led-upgrade = &led_diag_orange;
+	};
+
+	leds {
+		compatible = "gpio-leds";
+
+		wan_blue {
+			label = "tp-link:blue:wan";
+			gpios = <&gpio 14 GPIO_ACTIVE_LOW>;
+		};
+
+		led_diag_orange: diag_orange {
+			label = "tp-link:orange:diag";
+			gpios = <&gpio 15 GPIO_ACTIVE_HIGH>;
+			default-state = "on";
+		};
+	};
+};
+
+&eth1 {
+	mtd-mac-address = <&uboot 0x1fc00>;
+};

target/linux/ath79/image/tiny-tp-link.mk

@@ -274,6 +274,20 @@ define Device/tplink_tl-wr940n-v4
 endef
 TARGET_DEVICES += tplink_tl-wr940n-v4
 
+define Device/tplink_tl-wr940n-v6
+  $(Device/tplink-4mlzma)
+  SOC := tp9343
+  DEVICE_MODEL := TL-WR940N
+  DEVICE_VARIANT := v6
+  TPLINK_HWID := 0x09400006
+  SUPPORTED_DEVICES += tl-wr940n-v6
+  IMAGES += factory-us.bin factory-eu.bin factory-br.bin
+  IMAGE/factory-us.bin := tplink-v1-image factory -C US
+  IMAGE/factory-eu.bin := tplink-v1-image factory -C EU
+  IMAGE/factory-br.bin := tplink-v1-image factory -C BR
+endef
+TARGET_DEVICES += tplink_tl-wr940n-v6
+
 define Device/tplink_tl-wr941-v2
   $(Device/tplink-4m)
   SOC := ar9132

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

@@ -96,6 +96,9 @@ tplink,tl-wr941nd-v6)
 	ucidef_set_led_switch "lan3" "LAN3" "tp-link:blue:lan3" "switch0" "0x04"
 	ucidef_set_led_switch "lan4" "LAN4" "tp-link:blue:lan4" "switch0" "0x02"
 	;;
+tplink,tl-wr940n-v6)
+	ucidef_set_led_netdev "wan" "WAN" "tp-link:blue:wan" "eth1"
+	;;
 esac
 
 board_config_flush

target/linux/ath79/tiny/base-files/etc/board.d/02_network

@@ -48,6 +48,7 @@ ath79_setup_interfaces()
 	tplink,tl-wr841-v12|\
 	tplink,tl-wr940n-v3|\
 	tplink,tl-wr940n-v4|\
+	tplink,tl-wr940n-v6|\
 	tplink,tl-wr941nd-v6)
 		ucidef_set_interface_wan "eth1"
 		ucidef_add_switch "switch0" \