Changed "txpingpong" prop to "tx-ping-pong". Same for rx. This is done to
make the property name exactly match what is output by the xilinx tools for
this IP.
Signed-off-by: NPeter A. G. Crosthwaite <peter.crosthwaite@petalogix.com>
Signed-off-by: NEdgar E. Iglesias <edgar.iglesias@gmail.com>