ramips: add support for GeHua GHL-R-001

ramips: add support for GeHua GHL-R-001

Specs
	SoC: MT7621AT
	RAM: 512MiB
	Flash: 32MiB MX25L25635F SPI NOR
	2.4G: MT7603EN
	5G: MT7612EN
	Ethernet: 4x GE ports (1x WAN, 3x LAN) with link status LEDs
	USB 3.0
	LEDs: POWER, 5G WIFI, 2.4G WIFI, USB, Internet.
	      The last two ones are controlled by GPIO
	UART: There are 2 UARTs (UARTLITE1/ttyS0 and UARTLITE3/ttyS1) on board.
	      UARTLITE1 is close to LEDs, and UARTLITE3 is close to flash chip.
	      The stock u-boot uses UARTLITE1 by default. Baud rate is 57600

Flash instruction
	1. telnet 192.168.9.1 2317, username is "root" and password is "admin"
	   One can alternatively use UART to log in
	2. Put OpenWrt firmware in a FAT32 USB drive, and connect it to the router
	   One can alternatively download the firmware via wget through Internet
	3. mtd write /path/to/openwrt.bin firmware
	4. reboot

Signed-off-by: Deng Qingfang <dengqf6@mail2.sysu.edu.cn>