dma: Introduce dma_get_cfg() interface

dma: Introduce dma_get_cfg() interface

Sometimes, there would be a need to exchange data between DMA provider
and DMA client which are very specific to DMA driver of the SoC/platform
and are not generic enough to be put into struct dma. Therefore, introduce
dma_get_cfg() interface to get DMA provider specific data from client
device. Clients can use unique configuration ID flags to get different
configuration data from DMA driver.

Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
Reviewed-by: Grygorii Strashko <grygorii.strashko@ti.com>