dts: arm: rakwireless: add RAK3172 LoRaWAN module

Add DT definitions for the RAK3172 LoRaWAN module, based on
STM32WLE5.

Ref. https://docs.rakwireless.com/product-categories/wisduo/


             rak3172-module/low-level-development/

Signed-off-by: Gerard Marull-Paretas <gerard@teslabs.com>