dt-bindings: soc: xilinx: Add DT bindings to xlnx_vcu driver

Add Device Tree binding document for logicoreIP. This logicoreIP
provides the isolation between the processing system and
programmable logic. Also provides the clock related information.

Signed-off-by: Dhaval Shah <dshah@xilinx.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>