EDAC, mv64x60: Use platform_register/unregister_drivers()

These new helpers simplify implementing multi-driver modules and
properly handle failure to register one driver by unregistering all
previously registered drivers.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Cc: linux-edac <linux-edac@vger.kernel.org>
Link: http://lkml.kernel.org/r/1449073138-10852-2-git-send-email-thierry.reding@gmail.com
Signed-off-by: Borislav Petkov <bp@suse.de>