Add variable for checking channel idle state to ensure that dma
descriptor is not submitted when dmaengine is in progress.

This will avoid the polling for a bit in the status register to know
dma state in the driver hot path.
Reviewed-by: NJose Abreu <joabreu@synopsys.com>
Signed-off-by: NKedareswara rao Appana <appanad@xilinx.com>
Signed-off-by: NVinod Koul <vinod.koul@intel.com>