dt-bindings: Add LEGO MINDSTORMS EV3 compatible specification

[ Upstream commit 21078ab174c99885ca83a5c32db0d33b1617745e ]

This adds the board level device tree specification for LEGO MINDSTORMS EV3

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: David Lechner <david@lechnology.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>