dmaengine: dw: always export dw_dma_{en,dis}able

Instead of conditional exporing of dw_dma_suspend() / dw_dma_resume() let's
export dw_dma_disable() / dw_dma_enable(). Since dw_dma_shutdown() repeats
dw_dma_disable() we may safely remove it at all.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>