arm64: dts: meson: add libretech-pc boards support

Add support for the the amlogic libretech-pc platform, aka tartiflette.
There is 2 variants of the platform, one with the s905d, the other with
the s912.

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>