dt-bindings: amlogic: Add Internal Clock Measurer bindings

The Amlogic Meson SoCs embeds a clock measurer IP to measure the internal
clock paths frequencies.

Acked-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>