ARM: mvebu: update comments in coherency.c

The coherency.c top-level comment mentions that it supports the
coherency fabric for Armada 370 and XP, but it also supports the
coherency fabric on Armada 375 and 38x, so this commit updates the
comment accordingly.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Link: https://lkml.kernel.org/r/1415871540-20302-6-git-send-email-thomas.petazzoni@free-electrons.com
Signed-off-by: Jason Cooper <jason@lakedaemon.net>