drivers: dma: stm32: add missing fifo operation

The DMA driver of stm32 used to use `stm32_dma_enable_fifo()`,
which is located in dma_stm32_v1.c to set DMDIS bit, enable
interrupt generation and set FIFO threshold. Now since FIFO
threshold is initialized with `stm32_dma_get_fifo_threshold()`
and interrupt generation is also configured in dma_stm32.c, this
function will only have one job, to configure FIFO mode.
We can add FIFO mode operation in dma_stm32.c directly and
remove it from dma_stm32_v1.c.

Signed-off-by: Song Qiang <songqiang1304521@gmail.com>