ramips: add support for Netgear R6120

This patch adds support for the Netgear R6120, aka Netgear AC1200.

Specification:
- SoC: MediaTek MT7628 (580 MHz)
- Flash: 16 MiB
- RAM: 64 MiB
- Wireless: 2.4Ghz(builtin) and 5Ghz (MT7612E)
- LAN speed: 10/100
- LAN ports: 4
- WAN speed: 10/100
- WAN ports: 1
- Serial baud rate of Bootloader and factory firmware: 57600

To flash use nmrpflash with the provided factory.img.
Flashing via webinterface will not work, for now.

Signed-off-by: Ludwig Thomeczek <ledesrc@wxorx.net>

target/linux/ramips/image/mt76x8.mk

@@ -2,6 +2,17 @@
 # MT76x8 Profiles
 #
 
+DEVICE_VARS += SERCOMM_KERNEL_OFFSET SERCOMM_HWID SERCOMM_HWVER SERCOMM_SWVER
+
+define Build/mksercommfw
+	$(STAGING_DIR_HOST)/bin/mksercommfw \
+		$@ \
+		$(SERCOMM_KERNEL_OFFSET) \
+		$(SERCOMM_HWID) \
+		$(SERCOMM_HWVER) \
+		$(SERCOMM_SWVER)
+endef
+
 define Device/tplink
   TPLINK_FLASHLAYOUT :=
   TPLINK_HWID :=
@@ -91,6 +102,23 @@ define Device/mt7628
 endef
 TARGET_DEVICES += mt7628
 
+define Device/netgear_r6120
+  DTS := R6120
+  BLOCKSIZE := 64k
+  IMAGE_SIZE := $(ralink_default_fw_size_16M)
+  DEVICE_TITLE := Netgear AC1200 R6120
+  DEVICE_PACKAGES := kmod-usb2 kmod-usb-ohci
+  SERCOMM_KERNEL_OFFSET := 90000
+  SERCOMM_HWID := CGQ
+  SERCOMM_HWVER := A001
+  SERCOMM_SWVER := 0040
+  IMAGES += factory.img
+  IMAGE/default := append-kernel | pad-to $$$$(BLOCKSIZE)| append-rootfs | pad-rootfs
+  IMAGE/sysupgrade.bin := $$(IMAGE/default) | append-metadata | check-size $$$$(IMAGE_SIZE)
+  IMAGE/factory.img := $$(IMAGE/default) | mksercommfw
+endef
+TARGET_DEVICES += netgear_r6120
+
 define Device/omega2
   DTS := OMEGA2
   IMAGE_SIZE := $(ralink_default_fw_size_16M)