arm64: dts: meson-g12b: support a311d and s922x cpu operating points

Meson g12b ships with a low-speed (S922X) and high-speed (A311D) variant
so remove cpu_opp_table nodes in meson-g12b.dtsi and create two new dtsi
that can be included in device-specific dts files. Opp points were taken
from the vendor BSP kernel.

Also make meson-g12b-odroid-n2.dts include the new meson-g12b-s922x.dtsi.

Signed-off-by: Christian Hewitt <christianshewitt@gmail.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Kevin Hilman <khilman@baylibre.com>
Tested-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>