vdmatest: xilinx: Fix VDMA hang reported in certain resolutions

vdmatest: xilinx: Fix VDMA hang reported in certain resolutions

Avoid enabling circular_park mode for S2MM as it might happen that engine
continuously circles through frame buffers w/o being programmed and lead
to an undesired hang. In loopback it is recommended to use same park mode
configuration for both channels.

Signed-off-by: Radhey Shyam Pandey <radheys@xilinx.com>
Acked-by: Kedareswara rao Appana <appanad@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>