ramips: add support for ELECOM WRC-1167FS

ramips: add support for ELECOM WRC-1167FS

ELECOM WRC-1167FS is a 2.4/5 GHz band 11ac (WiFi-5) router, based on
MT7628AN.

Specification:

- SoC		: MediaTek MT7628AN
- RAM		: DDR2 64 MiB (NT5TU32M16FG-AC)
- Flash		: SPI-NOR 16 MiB (W25Q128JVSIQ)
- WLAN		: 2.4/5 GHz 2T2R
  - 2.4 GHz	: MediaTek MT7628AN (SoC)
  - 5 GHz	: MediaTek MT7612E
- Ethernet	: 10/100 Mbps x2
  - Switch	: MT7628AN (SoC)
- LEDs/Keys	: 6x, 3x (2x buttons, 1x slide-switch)
- UART		: through-hole on PCB
  - J1: 3.3V, GND, TX, RX from "J1" marking
  - 57600n8
- Power		: 12 VDC, 1 A

Flash instruction using factory image:

1. Boot WRC-1167FS normally
2. Access to "http://192.168.2.1/" and open firmware update page
   ("ファームウェア更新")
3. Select the OpenWrt factory image and click apply ("適用") button to
   perform firmware update
4. Wait ~120 seconds to complete flashing

Notes:

- Last 0x800000 (8 MiB) in SPI-NOR flash is not used on stock firmware

- Additional padding in factory image is required to avoid incomplete
  flashing on stock firmware

MAC addresses:

- LAN	: BC:5C:4C:xx:xx:68 (Config, ethaddr (text) / Factory, 0x28   (hex))
- WAN	: BC:5C:4C:xx:xx:69 (Config, wanaddr (text) / Factory, 0x22   (hex))
- 2.4GHz: BC:5C:4C:xx:xx:6A (Config, rmac    (text) / Factory, 0x4    (hex))
- 5GHz	: BC:5C:4C:xx:xx:6B (Config, rmac2   (text) / Factory, 0x8004 (hex))

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