dt-bindings: arm: amlogic: Move 'amlogic, meson-gx-ao-secure' binding to its own file

It is best practice to have 1 binding per file, so board level bindings
should be separate for various misc SoC bindings.

Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Carlo Caione <carlo@caione.org>
Cc: Kevin Hilman <khilman@baylibre.com>
Cc: devicetree@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-amlogic@lists.infradead.org
Signed-off-by: Rob Herring <robh@kernel.org>
Acked-by: Neil Armstrong <narmstrong@baylibre.com>
Acked-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>