drivers/dma: stm32: Preparation for QSPI DMA mode support

In preparation for QSPI DMA mode:
-Add a possibility to override driver by the HAL DMA. In that case
stream is set as busy and no configuration nor treatment is done.
In case of interrupt, flags clearing is let to HAL.
-Treat Half Transfer interrupt prior to Transfer Complete for the
cases were both IRQ are both raised at the time IRQ handler is called

Signed-off-by: Erwan Gouriou <erwan.gouriou@linaro.org>