ARM: mvebu: add SSCG to Armada 370 Device Tree

The Armada 370 SoC has a Spread Spectrum Clock Generator. This commit
adds the description of this generator to the Device Tree describing
this SoC.

Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Tested-by: Leigh Brown <leigh@solinno.co.uk>
Link: https://lkml.kernel.org/r/1409645719-20003-4-git-send-email-gregory.clement@free-electrons.com


Signed-off-by: Jason Cooper <jason@lakedaemon.net>