mips: dts: ralink: Add support for TP-Link HC220 G5 v1 board

This WiFi AP is based on a MT7621 SoC with 128MiB RAM, 128MiB NAND,
a MT7603 2.4GHz WiFi and a MT7613 5GHz WiFi chips integrated on the board,
connected to the main SoC over PCIe.

The device uses NMBM over NAND, which is not currently supported in the
mainline, so NAND node is skipped in this revision.

Signed-off-by: Liviu Dudau <liviu@dudau.co.uk>
Reviewed-by: Arınç ÜNAL <arinc.unal@arinc9.com>
Acked-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>