mediatek: filogic: add Netcore N60 support

mediatek: filogic: add Netcore N60 support

Hardware specification:
  SoC: MediaTek MT7986A 4x A53
  Flash: ESMT F50L1G41LB 128MB
  RAM: W632GU6NB DDR3 256MB
  Ethernet: 1x 2.5G + 4x 1G
  WiFi1: MT7975N 2.4GHz 4T4R
  WiFi2: MT7975PN 5GHz 4T4R
  Button: Reset, WPS
  Power: DC 12V 2A

Flash instructions:
  1. Connect to the router using ssh or telnet,
     username: useradmin, password is the web
     login password of the router.
  2. Use scp to upload bl31-uboot.fip and flash:
     "mtd write xxx-preloader.bin spi0.0"
     "mtd write xxx-bl31-uboot.fip FIP"
     "mtd erase ubi"
  3. Connect to the router via the Lan port,
     set a static ip of your PC.
     (ip 192.168.1.254, gateway 192.168.1.1)
  4. Download initramfs image, reboot router,
     waiting for tftp recovery to complete.
  5. After openwrt boots up, perform sysupgrade.

Note:
  1. Back up all mtd partitions before flashing.

Signed-off-by: Chukun Pan <amadeus@jmu.edu.cn>
(cherry picked from commit 4ae474afbd023a3386f4276ca8f948a44b49ff1b)