dt-bindings: add documentation of xilinx clocking wizard

Add the devicetree binding for the xilinx clocking wizard.

Signed-off-by: Shubhrajyoti Datta <shubhrajyoti.datta@xilinx.com>
Link: https://lore.kernel.org/r/20220411100443.15132-2-shubhrajyoti.datta@xilinx.com


Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>