dt-bindings: arm: amlogic: Add the Endless Mobile Endless Mini (EC-100)

Add bindings documentation for the Endless Mini (EC-100) from Endless
Mobile.

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