arm64: dts: specify console via command line

arm64: dts: specify console via command line

The SPRD serial driver need to know which serial port would be used as
console in an early period during initialization, otherwise console
init would fail since we added this feature[1].

So this patch add console to command line via devicetree.

[1] https://lore.kernel.org/lkml/20190826072929.7696-4-zhang.lyra@gmail.com/

Link: https://lore.kernel.org/r/20200311112120.30890-1-zhang.lyra@gmail.com
Signed-off-by: Chunyan Zhang <chunyan.zhang@unisoc.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>