Add the device tree for ASUS RT-AC5300 which is an AC5300 router featuring
5 Ethernet ports over the integrated Broadcom switch.

Hardware info:
* Processor: Broadcom BCM4709C0 dual-core @ 1.4 GHz
* Switch: BCM53012 in BCM4709C0
* DDR3 RAM: 512 MB
* Flash: 128 MB
* 2.4GHz: BCM4366 4x4 single chip 802.11b/g/n SoC
* 5GHz: BCM4366 4x4 two chips 802.11a/n/ac SoC
* Ports: 4 LAN Ports, 1 WAN Port
Co-developed-by: Tom Brautaset <tbrautaset@gmail.com>
Signed-off-by: Tom Brautaset <tbrautaset@gmail.com>
Signed-off-by: Arınç ÜNAL <arinc.unal@arinc9.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20240423-for-soc-asus-rt-ac3200-ac5300-v3-4-23d33cfafe7a@arinc9.comSigned-off-by: Florian Fainelli <florian.fainelli@broadcom.com>