ARM: tegra: Add stdout-path for various boards

For Tegra boards, the device-tree alias serial0 is used for the console
and so add the stdout-path information so that the console no longer
needs to be passed via the kernel boot parameters.

This has been tested on boards, tegra20-trimslice, tegra30-beaver,
tegra114-dalmore and tegra124-jetson-tk1.

Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Acked-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Thierry Reding <treding@nvidia.com>