ath79: add support for ZyXEL NWA1123-AC

Specifications:
 * AR9342, 16 MiB Flash, 64 MiB RAM, 802.11n 2T2R, 2.4 GHz
 * QCA9882 PCIe card, 802.11ac 2T2R
 * 1x Gigabit Ethernet (AR8035), 802.3af PoE

Installation:
* OEM Web UI is at 192.168.1.2
  login as `admin` with password `1234`
* Flash factory-AAOX.bin

The string `AAOX` needs to be present within the file name of the uploaded
image to be accepted by the OEM Web-based updater, the factory image is
named accordingly to save the user from the hassle of manual renaming.

TFTP Recovery:
* Open the case, connect to TTL UART port (this is the official method
  described by Zyxel, the reset button is useless during power-on)
* Extract factory image (.tar.bz2), serve `vmlinux_mi124_f1e.lzma.uImage`
  and `mi124_f1e-jffs2` via tftp at 192.168.1.10
* Interrupt uboot countdown, execute commands
  `run lk`
  `run lf`
  to flash the kernel / filesystem accordingly

MAC addresses as verified by OEM firmware:
use   address   source
LAN   *:1c      mib0 0x30 ('eth0mac'), art 0x1002 (label)
2g    *:1c      mib0 0x4b ('wifi0mac')
5g    *:1e      mib0 0x66 ('wifi1mac')

Signed-off-by: Sebastian Schaper <openwrt@sebastianschaper.net>

target/linux/ath79/dts/ar9342_zyxel_nwa1123-ac.dts

@@ -0,0 +1,35 @@
+// SPDX-License-Identifier: GPL-2.0-or-later OR MIT
+
+#include "ar9342_zyxel_nwa11xx.dtsi"
+
+/ {
+	compatible = "zyxel,nwa1123-ac", "qca,ar9342";
+	model = "Zyxel NWA1123-AC";
+
+	aliases {
+		label-mac-device = &eth0;
+		led-boot = &led_status_green;
+		led-failsafe = &led_status_amber;
+		led-running = &led_status_green;
+		led-upgrade = &led_status_amber;
+	};
+
+	leds {
+		compatible = "gpio-leds";
+
+		led_status_green: status_green {
+			label = "green:status";
+			gpios = <&gpio 12 GPIO_ACTIVE_LOW>;
+			default-state = "on";
+		};
+
+		led_status_amber: status_amber {
+			label = "amber:status";
+			gpios = <&gpio 11 GPIO_ACTIVE_LOW>;
+		};
+	};
+};
+
+&pcie {
+	status = "okay";
+};