arm64: dts: apm: Update X-Gene standby GPIO controller DTS entries

Update APM X-Gene standby GPIO controller DTS entries to enable it
as interrupt controller.

[dhdang: update patch subject]
Signed-off-by: Y Vo <yvo@apm.com>
Signed-off-by: Quan Nguyen <qnguyen@apm.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Duc Dang <dhdang@apm.com>