dt-bindings: xilinx: zynq: Sort entries alphabetically

Sort additional compatible strings (boards) alphabetically
by their manufacturer and model number

This will help when finding a board because they
will be grouped by their manufacturer

Signed-off-by: Luis Araneda <luaraneda@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>