Add device_prep_slave_sg() callback function so that DMA_MEM_TO_DEV
and DMA_DEV_TO_MEM operations in single mode can be supported.

Existing AxiDMA driver only support data transfer between
memory to memory. Data transfer between device to memory and
memory to device in single mode would failed if this interface
is not supported by the AxiDMA driver.
Signed-off-by: Sia Jee Heng <jee.heng.sia@intel.com>
Tested-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Link: https://lore.kernel.org/r/20210125013255.25799-7-jee.heng.sia@intel.comSigned-off-by: Vinod Koul <vkoul@kernel.org>