configs/zynqmp_zcu10x: fix U-Boot dts config

Add a U-Boot config fragment to set the correct control device tree file for
each board, rather than using the default (zcu100).

Signed-off-by: Neal Frager <neal.frager@xilinx.com>
Tested-by: Peter Korsgaard <peter@korsgaard.com>
[Peter: reword commit message, rename fragment files]
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>