dts: arm: stm32 devices with xspi is named spi node

Fixes the CMake Warning on build/zephyr/zephyr.dts:
Warning (spi_bus_bridge): /soc/xspi@47001400: node name
for SPI buses should be 'spi'

Signed-off-by: Francois Ramu <francois.ramu@st.com>