intel_mid_dma: Allow IRQ sharing

intel_mid_dma driver allows interrupt sharing. Thus it needs
to check whether IRQ source is the DMA controller and return
the appropriate IRQ return.

Signed-off-by: Yong Wang <yong.y.wang@intel.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>