ARM: dts: BCM5301X: Add support for Buffalo WXR-1750DHP

ARM: dts: BCM5301X: Add support for Buffalo WXR-1750DHP

Add initial device tree support for the Buffalo WXR-1750DHP, a consumer Wi-Fi
router based on the Broadcom BCM4708A0 SoC.

Hardware specifications:
* Processor: Broadcom BCM4708A0 dual-core @ 800 MHz
* RAM: DDR3 256 MB
* Ethernet Switch: Broadcom BCM53011 integrated via SRAB
* NAND Flash: 128 MB (8-bit ECC)
* SPI Flash: None
* Ports: 4 LAN Ports, 1 WAN Port
* USB: 1x USB 3.0 Type-A port

Signed-off-by: Taishi Shimizu <s.taishi14142@gmail.com>
Link: https://lore.kernel.org/r/20250713071826.726682-3-s.taishi14142@gmail.com
Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>