bmips: add support for Sagem F@ST3864OP

bmips: add support for Sagem F@ST3864OP

Specifications:
* SoC: BCM63168
* RAM: NT5CC64M16GP-DI, DDR3 128MiB
* NAND: W29N01HVSINA, 128MiB
* Ethernet: 4x1000M LAN, 1x 1000M WAN
* Serial interface: on board but not populated, 3.3V, 115200, 8N1

Notes:
* Use DSA for VLAN and switches
* Ethernet ports and USB works
* gpio-leds are not working
* WLAN, xDSL, and FXS are not going to work

Signed-off-by: Hang Zhou <929513338@qq.com>
[refactor, reorder, drop unneeded or not working stuff]
Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>