irqchip: vf610-mscm: Add Vybrid MSCM bindings

Add binding documentation for CPU configuration and interrupt router
submodule of the Miscellaneous System Control Module. The MSCM is
used in all variants of Freescale Vybrid SoC's.

Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Stefan Agner <stefan@agner.ch>
Link: https://lkml.kernel.org/r/1425249689-32354-3-git-send-email-stefan@agner.ch
Signed-off-by: Jason Cooper <jason@lakedaemon.net>