dt-bindings: gpio: gpio-xilinx: Mark clocks as required property

dt-bindings: gpio: gpio-xilinx: Mark clocks as required property

On Microblaze platforms there is no need to handle clocks because the
system is starting with clocks enabled (can be described via fixed clock
node or clock-frequency property or not described at all).
With using soft IPs with SOC platforms there is mandatory to handle clocks
as is explained in commit 60dbdc6e08d6 ("dt-bindings: net: emaclite: Add
clock support").
That's why make clock as required in dt binding because it is present in
both configurations and should be described even there is no way how to
handle it on Microblaze systems.

There is also need to describe missing axi gpio clock in fpga-region.yaml
not to introduce new error when make dt_binding_check runs.

Signed-off-by: Michal Simek <michal.simek@amd.com>
Reviewed-by: Xu Yilun <yilun.xu@intel.com> # fpga
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/94151cfbcff5e4ae05894981c7e398b605d4b00a.1750059796.git.michal.simek@amd.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>