dmaengine: idma64: Support dmaengine_terminate_sync()

It appears that the driver misses the support of dmaengine_terminate_sync().
Since many of callers expects this behaviour implement the new
device_synchronize() callback to allow proper synchronization when stopping
a channel.

Fixes: b36f09c3 ("dmaengine: Add transfer termination synchronization support")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Vinod Koul <vkoul@kernel.org>