dt-bindings: altera: Add enclustra mercury PE1

Add binding for the enclustra PE1 baseboard from enclustra GmbH.

Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Steffen Trumtrar <s.trumtrar@pengutronix.de>
Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>