dma: ti: k3-udma: Implement dma_get_cfg() interface

dma: ti: k3-udma: Implement dma_get_cfg() interface

Implement dma_get_cfg() interface to pass flow id information for DMA
clients to use. This is needed because on K3 SoCs, CPSW (ethernet) and
UDMA (DMA provider) support "flows" within a given RX DMA channel. This
allows different network packets to be segregated while using same RX
DMA channel. In order for basic ethernet to work, CPSW slave must be
aware of the flow ID allocated for the RX channel by the DMA driver.
This interface allows CPSW to query flow ID from DMA provider and
configure it in CPSW HW.

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