dt-bindings: gpio: gpio-xilinx: Convert Xilinx axi gpio binding to YAML

Convert Xilinx axi gpio binding documentation to YAML.

Signed-off-by: Srinivas Neeli <srinivas.neeli@xilinx.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>