drivers: i2s_sam_ssc: use `dma_reload()` to continue transfer

Use `dma_reload()` instead of `dma_config()` within DMA callbacks. This
significantly shortens time required to reconfigure DMA engine to
transmit / receive the next data block and allows to configure higher
I2S bus data rates.

The maximum I2S data rate supported by the driver is still lower than
that of underlying hardware. To fully support hardware capabilities the
I2S driver would have to use scatter-gather / linked-list DMA transfer.
This is currently not supported by the DMA driver.

Signed-off-by: Piotr Mienkowski <piotr.mienkowski@gmail.com>