ramips: add support for ELECOM WRC-2533GST

ELECOM WRC-2533GST is a 2.4/5 GHz band 11ac rotuer, based on
MediaTek MT7621A.

Specification:

- MT7621A (2-Core, 4-Threads)
- 128 MB of RAM (DDR3)
- 16 MB of Flash (SPI)
- 4T4R 2.4/5 GHz wifi
  - MediaTek MT7615
- 5x 10/100/1000 Mbps Ethernet
- 4x LEDs, 6 keys (2x buttons, 1x slide switch)
- UART header on PCB
  - Vcc, GND, TX, RX from ethernet port side
  - baudrate: 57600 bps

Flash instruction using factory image:

1. Connect the computer to the LAN port of WRC-2533GST
2. Connect power cable to WRC-2533GST and turn on it
3. Access to "https://192.168.2.1/" and open firmware update
page ("ファームウェア更新")
4. Select the OpenWrt factory image and click apply ("適用")
button
5. Wait ~150 seconds to complete flashing

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

target/linux/ramips/image/mt7621.mk

@@ -4,6 +4,19 @@
 
 DEVICE_VARS += TPLINK_BOARD_ID TPLINK_HEADER_VERSION TPLINK_HWID TPLINK_HWREV
 
+define Build/elecom-gst-factory
+  $(eval product=$(word 1,$(1)))
+  $(eval version=$(word 2,$(1)))
+  ( $(STAGING_DIR_HOST)/bin/mkhash md5 $@ | tr -d '\n' ) >> $@
+  ( \
+    echo -n "ELECOM $(product) v$(version)" | \
+      dd bs=32 count=1 conv=sync; \
+    dd if=$@; \
+  ) > $@.new
+  mv $@.new $@
+  echo -n "MT7621_ELECOM_$(product)" >> $@
+endef
+
 define Build/elecom-wrc-factory
   $(eval product=$(word 1,$(1)))
   $(eval version=$(word 2,$(1)))
@@ -104,6 +117,16 @@ define Device/elecom_wrc-1167ghbk2-s
 endef
 TARGET_DEVICES += elecom_wrc-1167ghbk2-s
 
+define Device/elecom_wrc-2533gst
+  DTS := WRC-2533GST
+  IMAGE_SIZE := 11264k
+  DEVICE_TITLE := ELECOM WRC-2533GST
+  IMAGES += factory.bin
+  IMAGE/factory.bin := $$(sysupgrade_bin) | check-size $$$$(IMAGE_SIZE) |\
+    elecom-gst-factory WRC-2533GST 0.00
+endef
+TARGET_DEVICES += elecom_wrc-2533gst
+
 define Device/ew1200
   DTS := EW1200
   IMAGE_SIZE := $(ralink_default_fw_size_16M)