dt-bindings: serial: amlogic, meson-uart: support S4

Add serial bindings support menson S4 SoC family.

Signed-off-by: Xianwei Zhao <xianwei.zhao@amlogic.com>
Link: https://lore.kernel.org/r/20211221030146.522-1-xianwei.zhao@amlogic.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>