ramips: add support for cudy WR2100

ramips: add support for cudy WR2100

Specifications

  SoC:       MT7621
  CPU:       880 MHz
  Flash:     16 MiB
  RAM:       128 MiB
  WLAN:      2.4 GHz b/g/n, 5 GHz a/n/ac
             MT7603E / MT7615E
  Ethernet:  5x Gbit ports

Installation

There are two known options:
1) The Luci-based UI.
2) Press and hold the reset button during power up.
   The router will request 'recovery.bin' from a TFTP server at
   192.168.1.88.

Both options require a signed firmware binary.
The openwrt image supplied by cudy is signed and can be used to
install unsigned images.

R4 & R5 need to be shorted (0-100Ω) for the UART to work.

Signed-off-by: Leon M. George <leon@georgemail.eu>
[remove non-required switch-port node - remove trgmii phy-mode]
Signed-off-by: David Bauer <mail@david-bauer.net>
(cherry picked from commit 3501db9b9b4a71ae52c539b46af817783c327866)