arm64: dts: meson-gx: add ATF BL32 reserved-memory region

Add an additional reserved memory region for the BL32 trusted firmware
present in many devices that boot from Amlogic vendor u-boot.

Suggested-by: Mateusz Krzak <kszaquitto@gmail.com>
Signed-off-by: Christian Hewitt <christianshewitt@gmail.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://lore.kernel.org/r/20220126044954.19069-2-christianshewitt@gmail.com