dt-bindings: tegra186-gpio: Add information for Tegra194

The Tegra194 GPIO controller is similar to the one in Tegra186.
Add relevant information to the device tree binding documentation.

Signed-off-by: Mikko Perttunen <mperttunen@nvidia.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>