dma: dmaengine: add slave req id in slave_config

The DMA controller like Nvidia's Tegra Dma controller
supports the different slave requestor id from different slave.
This need to be configure in dma controller to handle the request
properly.

Adding the slave-id in the slave configuration so that information
can be passed from client when configuring for slave.

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Signed-off-by: Vinod Koul <vinod.koul@linux.intel.com>