dt-bindings: timestamp: Add Tegra234 support

Added timestamp provider support for the Tegra234 in devicetree
bindings. From Tegra234 SoC onwards, the nvidia,gpio-controller
property is required. This is needed as the tegra always-on (AON) GPIO
HTE/GTE provider depends on the AON GPIO controller where it needs to
do namespace conversion between GPIO line number (belonging to AON
GPIO controller instance) and the GTE slice bits.

Signed-off-by: Dipen Patel <dipenp@nvidia.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>