dma: dw_dmac: add dwc_chan_pause and dwc_chan_resume

We will use at least the dwc_chan_resume() later.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>