ARM: dts: add Protonic PRTI6Q board

Protonic PRTI6Q is a development board and a base class for different
specific customer application boards based on the i.MX6 family of SoCs,
developed by Protonic Holland.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: David Jander <david@protonic.nl>
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>