ramips: mt76x8: add support for Yuncore CPE200

ramips: mt76x8: add support for Yuncore CPE200

Yuncore CPE200 is an outdoor unit with IEEE 802.11ac radio.

Hardware:
 - SoC: MediaTek MT7628DAN (MIPS 580MHz)
 - Flash: 8 MiB Spansion S25FL064K
 - RAM: 64 MiB (built-into SoC)
 - WLAN: 5 GHz (MT7613AE)
 - Ethernet: 1x 10/100 Mbps WAN, 1x 10/100 LAN (MT7628)
 - Buttons: 1 Reset button, 2 buttons for display UI (unsupported)
 - LEDs: 4x Green (Power, LAN, WAN, WiFi)
 - Display: 4 digit 7-segment display driven by an additional
            microcontroller (unsupported)
 - Serial console: unpopulated header, 57600 8n1 (RX only)
 - Power: 12 VDC, 1 A

Installation:
The installation can be done via the recovery HTTP server which is built
into the bootloader. Hold down the reset button while connecting the
device to power and keep holding a bit more than 3 seconds. Connect to
http://192.168.0.100/ and upload sysupgrade.bin file.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>