arm64: dts: meson-g12b: move common node into new odroid.dtsi

In order to introduce Odroid-N2L which is basically an Odroid-N2+
without some on-board peripherals (Ethernet, RTC, Hub, Jack),
move the common nodes into a new meson-g12b-odroid.dtsi which will
will be the common dtsi for all the Odroid-N2 derived boards.

Link: https://lore.kernel.org/r/20230122-topic-odroid-n2l-upstream-initial-v2-2-8d3fea6d403d@linaro.org


Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>