dt-bindings: serial: Add bindings for nvidia,tegra194-tcu

Add bindings for the Tegra Combined UART device used to talk to the
UART console on Tegra194 systems.

Signed-off-by: Mikko Perttunen <mperttunen@nvidia.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Jon Hunter <jonathanh@nvidia.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>