dmaengine: fsl-edma: add PM suspend/resume support

This add power management suspend/resume support for the fsl-edma
driver.

eDMA acted as a basic function used by others. What it needs to do
is the two steps below to support power management.

In fsl_edma_suspend_late:
Check whether the DMA chan is idle, if it is not idle disable DMA
request.

In fsl_edma_resume_early:
Enable the eDMA and wait for being used.

Signed-off-by: Yuan Yao <yao.yuan@freescale.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>