ARM: mvebu: use input DT defines in Armada 370/XP boards

Instead of harcoding keycodes specifications in the Armada 370/XP
boards, use the <dt-bindings/input/input.h> header file and its
keycode definitions.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>