dmaengine: xilinx_dma: Check for channel idle state before submitting dma descriptor

dmaengine: xilinx_dma: Check for channel idle state before submitting dma descriptor

Add variable for checking channel idle state to ensure that dma descriptor is not
Submitted when DMA engine is in progress.

This will avoids the pollling for a bit in the status register to know
Dma state in the driver hot path.

Reviewed-by: Jose Abreu <joabreu@synopsys.com>
Signed-off-by: Kedareswara rao Appana <appanad@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>