dmaengine: tegra-apb: Save and restore word count

Newer tegra devices have a separate word count register per channel that
contains the number of words to be transferred. This register is not
saved or restored by the suspend/resume helpers for these newer devices
and so ensure that it is.

Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>