xilinx: mbv: Use separate DTB for binman nodes

xilinx: mbv: Use separate DTB for binman nodes

The commit d92fdb60677b ("binman: Add option for pointing to separate
description") added support for separating binman description to own file
not the be the part of DT for OS.
The main reason is that binman is not passing dt schema validation that's
why want to keep it separated.

Signed-off-by: Michal Simek <michal.simek@amd.com>
Acked-by: Leo Yu-Chi Liang <ycliang@andestech.com>