ramips: add support for ELECOM WRC-1167GHBK2-S

ELECOM WRC-1167GHBK2-S is a 2.4/5 GHz band 11ac router, based on
MediaTek MT7621A.

Specification:

- MT7621A (2-Cores, 4-Threads)
- 128 MB of RAM (DDR3)
- 16 MB of Flash (SPI)
- 2T2R 2.4/5 GHz
  - MediaTek MT7615D
- 5x 10/100/1000 Mbps Ethernet
- 6x LEDs, 2x keys
- UART header on PCB
  - Vcc, GND, TX, RX from ethernet port side
  - baudrate: 57600 bps

Flash instruction using factory image:

1. Rename the factory image to "wrc-1167ghbk2-s_v0.00.bin"
2. Connect the computer to the LAN port of WRC-1167GHBK2-S
3. Connect power cable to WRC-1167GHBK2-S and turn on it
4. Access to "http://192.168.2.1/details.html" and open firmware
update page ("手動更新（アップデート）")
5. Select the factory image and click apply ("適用") button
6. Wait ~150 seconds to complete flashing

Signed-off-by: INAGAKI Hiroshi <musashino.open@gmail.com>

target/linux/ramips/image/mt7621.mk

@@ -4,6 +4,18 @@
 
 DEVICE_VARS += TPLINK_BOARD_ID TPLINK_HEADER_VERSION TPLINK_HWID TPLINK_HWREV
 
+define Build/elecom-wrc-factory
+  $(eval product=$(word 1,$(1)))
+  $(eval version=$(word 2,$(1)))
+  $(STAGING_DIR_HOST)/bin/mkhash md5 $@ >> $@
+  ( \
+    echo -n "ELECOM $(product) v$(version)" | \
+      dd bs=32 count=1 conv=sync; \
+    dd if=$@; \
+  ) > $@.new
+  mv $@.new $@
+endef
+
 define Build/ubnt-erx-factory-image
 	if [ -e $(KDIR)/tmp/$(KERNEL_INITRAMFS_IMAGE) -a "$$(stat -c%s $@)" -lt "$(KERNEL_SIZE)" ]; then \
 		echo '21001:6' > $(1).compat; \
@@ -65,6 +77,16 @@ define Device/mediatek_ap-mt7621a-v60
 endef
 TARGET_DEVICES += mediatek_ap-mt7621a-v60
 
+define Device/elecom_wrc-1167ghbk2-s
+  DTS := WRC-1167GHBK2-S
+  IMAGE_SIZE := 15488k
+  DEVICE_TITLE := ELECOM WRC-1167GHBK2-S
+  IMAGES += factory.bin
+  IMAGE/factory.bin := $$(sysupgrade_bin) | check-size $$$$(IMAGE_SIZE) |\
+    elecom-wrc-factory WRC-1167GHBK2-S 0.00
+endef
+TARGET_DEVICES += elecom_wrc-1167ghbk2-s
+
 define Device/ew1200
   DTS := EW1200
   IMAGE_SIZE := $(ralink_default_fw_size_16M)