With recent improvements to serial/of core from Grant and Rob,
stdout-path alone suffices for setting up earlycon/console.

arc_uart driver is already equipped to handle that, switch the DT now.
Signed-off-by: NVineet Gupta <vgupta@synopsys.com>
Reviewed-by: NRob Herring <robh@kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>