drivers: spi: stm32 spi instance of stm32H7 mcu

A generic function is used to give the register address to the DMA.
The SPI of the stm32H7 serie has two data registers for Tx and Rx
When the DMA is getting the address it differs between Rx and Tx.
As the stm32cube/stm32h7xx/drivers/include/stm32h7xx_ll_spi.h
has no such LL functions, the register address is get direclty.

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