ramips: add support for NETGEAR WAC124

The WAC124 hardware appears to be identical to R6260/R6350/R6850.

SoC:   MediaTek MT7621AT
RAM:   128M DDR3
FLASH: 128M NAND (Macronix MX30LF1G18AC)
WiFI:  MediaTek MT7603 bgn 2T2R
       MediaTek MT7615 nac 4T4R
ETH:   SoC Integrated Gigabit Switch (1x WAN, 4x LAN)
USB:   1x USB 2.0
BTN:   Reset, WPS
LED:   Power, Internet, WiFi, USB (all green)

Installation:
The factory image can be flashed from the stock firmware web interface
or using nmrpflash. With nmrpflash it is also possible to revert to
stock firmware.

Signed-off-by: Jan Hoffmann <jan@3e8.eu>

target/linux/ramips/dts/mt7621_netgear_wac124.dts

+// SPDX-License-Identifier: GPL-2.0-only
+/dts-v1/;
+
+#include "mt7621_netgear_sercomm_chj.dtsi"
+
+/ {
+	compatible = "netgear,wac124", "mediatek,mt7621-soc";
+	model = "Netgear WAC124";
+};
+
+&led_power {
+	label = "wac124:green:power";
+};
+
+&led_usb {
+	label = "wac124:green:usb";
+};
+
+&led_internet {
+	label = "wac124:green:wan";
+};
+
+&led_wifi {
+	label = "wac124:green:wifi";
+};

target/linux/ramips/image/mt7621.mk

@@ -702,6 +702,18 @@ define Device/netgear_wac104
 endef
 TARGET_DEVICES += netgear_wac104
 
+define Device/netgear_wac124
+  $(Device/netgear_sercomm_nand)
+  DEVICE_MODEL := WAC124
+  SERCOMM_HWNAME := WAC124
+  SERCOMM_HWID := CTL
+  SERCOMM_HWVER := A003
+  SERCOMM_SWVER := 0x0402
+  IMAGE_SIZE := 40960k
+  DEVICE_PACKAGES += kmod-mt7615e kmod-mt7615-firmware
+endef
+TARGET_DEVICES += netgear_wac124
+
 define Device/netgear_wndr3700-v5
   $(Device/uimage-lzma-loader)
   BLOCKSIZE := 64k

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

@@ -56,6 +56,7 @@ netgear,r6220|\
 netgear,r6260|\
 netgear,r6350|\
 netgear,r6850|\
+netgear,wac124|\
 netgear,wndr3700-v5)
 	ucidef_set_led_netdev "wan" "wan" "$boardname:green:wan" "wan"
 	;;

target/linux/ramips/mt7621/base-files/lib/upgrade/platform.sh

@@ -53,6 +53,7 @@ platform_do_upgrade() {
 	netgear,r6800|\
 	netgear,r6850|\
 	netgear,wac104|\
+	netgear,wac124|\
 	netis,wf2881|\
 	xiaomi,mir3g|\
 	xiaomi,mir3p|\