ARM64: dts: meson-gxl: Add support for HwaCom AmazeTV

This patch adds support for the HwaCom AmazeTV set-top-box. The
hardware configuration is really similar to the other GXL boards but
for this hardware we need to limit the max-frequency of the eMMC to
have it working.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Carlo Caione <carlo@endlessm.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>