ARM: dts: imx7d: move input header into base device tree

The base device tree uses KEY_POWER in the snvs-powerkey node,
hence include the input.h header file in the base device tree.

Signed-off-by: Stefan Agner <stefan@agner.ch>
Acked-by: Igor Grinberg <grinberg@compulab.co.il>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>