intel_mid_dma: Add runtime PM support

This patch adds runtime PM support in this dma driver
for 4 PCI Controllers
Whenever the driver is idle (no channels grabbed), it
can go to low power state
It also adds the PCI suspend and resume support

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>