media: xilinx: dma: Add vidioc_enum_fmt_vid_cap callback

Add vidioc_enum_fmt_vid_cap callback to enumerate the proper format
to user.

Signed-off-by: Hyun Kwon <hyunk@xilinx.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>