dmaengine: edma: Merge map_dmach_to_queue into assign_channel_eventq

edma_assign_channel_eventq() is a wrapper around edma_map_dmach_to_queue()
We can merge the content of the later so we will have only one function
to be used for mapping channels to given eventq

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>