pinctrl: Add Tegra194 pinctrl DT bindings

Add binding doc for Tegra 194 pinctrl driver.

Signed-off-by: Krishna Yarlagadda <kyarlagadda@nvidia.com>
Tested-by: Vidya Sagar <vidyas@nvidia.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>