ramips: add support for TP-Link RE650 v1

ramips: add support for TP-Link RE650 v1

TP-Link RE650 v1 is a dual-band AC2600 range extender,
based on MediaTek MT7621A and MT7615E. According to the
wikidevi entry for RE650 this device is identical with
TP-Link RE500 as hardware. This patch supports only RE650.

Hardware specification:

- SoC 880 MHz - MediaTek MT7621AT
- 128 MB of DDR3 RAM
- 16 MB - Winbond 25Q128FVSG
- 4T4R 2.4 GHz - MediaTek MT7615E
- 4T4R 5 GHz - MediaTek MT7615E
- 1x 1 Gbps Ethernet - MT7621AT integrated
- 7x LEDs (Power, 2G, 5G, WPS(x2), Lan(x2))
- 4x buttons (Reset, Power, WPS, LED)
- UART header (J1) - 2:GND, 3:RX, 4:TX
  Serial console @ 57600,8n1

Flash instructions:

Upload
openwrt-ramips-mt7621-tplink_re650-v1-squashfs-factory.bin
from the RE650 web interface.

TFTP recovery to stock firmware:

Unfortunately, I can't find an easy way to recover the RE
without opening the device and using modified binaries. The
TFTP upload will only work if selected from u-boot, which
means you have to open the device and attach to the serial
console. The TFTP update procedure does *not* accept the
published vendor firmware binaries. However, it allows to
flash kernel + rootfs binaries, and this works if you have
a backup of the original contents of the flash. It's probably
possible to create special image out of the vendor binaries
and use that as recovery image.

Signed-off-by: Georgi Vlaev <georgi.vlaev@gmail.com>
[re-added variables for kernel header]
Signed-off-by: David Bauer <mail@david-bauer.net>