arm64: dts: meson-gx: Add Internal Clock Measurer node

The Amlogic Meson GX SoCs embeds a clock measurer IP to measure the internal
clock paths frequencies.
This patch adds the node in the top-level meson-gx dtsi.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Acked-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>