drivers: spi: stm32 driver with dma checking spi busy status flag

Defines a function to control the spi busy state during DMA transfer.
After the DMA Tx, the spi might still have some data to Transmit.
The driver must wait for the SPI Tx before sending the next packet.
This is not required for the Rx part as the DMA Rx is already done.
Some mcus like stm32H7 have a TX complete bit, other must wait for the
TXE and BSY line.

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