arm64: tegra: Enable UART instance on 40-pin header

On P3737 board, UART-A is available on 40-pin header. Enable UART-A for
P3737 and change the compatible string to "nvidia,tegra194-hsuart". This
allows supporting HW flow control and is the preferred choice for higher
baud rates.

Signed-off-by: kartik <kkartik@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>