dts: stm32wl: define a subghz-spi radio node
dts: stm32wl: define a subghz-spi radio node

Add a device node for the subghz radio in stm32wl.dtsi. The radio is
present in all chips of the series, so having the node there with the
common properties simplifies the board dts files.

Signed-off-by: Fabio Baltieri <161d407f4dc681bfd4aedb33b8273b2aafd727bc@gmail.com>

zephyrproject-rtos/zephyr,galak/zephyr,finikorg/zephyr,galak/zephyr,finikorg/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,galak/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,galak/zephyr