drivers: spi: st_stm32: Abstract LL function for spi ver. compatibility

Abstract some SPI LL function call for future driver compatibility with
a new SPI peripheral version (introduced with STM32MP1x and STM32H7x
SoC)

Signed-off-by: Yaël Boutreux <yael.boutreux@st.com>
Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@st.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>