Blackfin: cleanup sync handling when enabling/disabling cplbs

The handling of updating the [DI]MEM_CONTROL MMRs does not follow proper
sync procedures as laid out in the Blackfin programming manual.  So rather
than audit/fix every call location, create helper functions that do the
right things in order to safely update these MMRs.  Then convert all call
sites to use these new helper functions.

While we're fixing the code, drop the workaround for anomaly 05000125 as
that anomaly applies to old versions of silicon that we do not support.

Signed-off-by: Yi Li <yi.li@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>