dma: dw: Poll to check for channel disable with timeout

After disabling the channel, it is recommended to poll with timeout to
ensure that the channel has actually been disabled. Without this,
reconfiguring the DMA again while the channel is active could lead to
unexpected behavior and/or DMA underruns.

Signed-off-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>