dt-bindings: altera: document existing Cyclone 5 board compatibles

Several Cyclone 5 SoCFPGA based boards have additional board compatibles
which are not documented in the bindings.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>