ARM: dts: Import libretech-ac DT from Linux 5.0

Import Linux 5.0 DT from 1c163f4c7b3f ("Linux 5.0") for the
meson-gxl-s805x-libretech-ac board and the corresponding changes
in meson-gxl.dtsi.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>