dmaengine: xilinx: dpdma: Add debugfs support

Expose statistics to debugfs when available. This helps debugging issues
with the DPDMA driver.

Signed-off-by: Hyun Kwon <hyun.kwon@xilinx.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Link: https://lore.kernel.org/r/20200812171228.9751-1-laurent.pinchart@ideasonboard.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>