ramips: add TP-LINK TL-WR902AC v4

Seems to be very similar to: https://openwrt.org/toh/tp-link/tl-wr902ac_v3
1 x usb
1 x eth
Powered by mini usb port.

Installation:

Can use TFTP method to install:
1. establish TFTP server at 192.168.0.66
2. provide tp_recover.bin file to the TFTP server
3. turn on router with reset button pressed
4. wait for led blinking, then release reset

Specification based on dmesg from already flashed device:

SoC Type: MediaTek MT7628AN ver:1 eco:2
CPU0 revision is: 00019655 (MIPS 24KEc)
Memory: 56028K/65536K available
CPU Clock: 580MHz
WiFi: MT7613BE

MAC addresses are all the same, except wifi5g which last part is decrement by one, ie.:

eth0		40:ed:00:cf:b9:9b
br-lan		40:ed:00:cf:b9:9b
phy0-ap0	40:ed:00:cf:b9:9b
phy1-ap0	40:ed:00:cf:b9:9a

Signed-off-by: Kamil Jońca <kjonca@onet.pl>