uboot-imx

aspeed: Make SCU lock/unlock functions part of SCU API

Make functions for locking and unlocking SCU part of SCU API.
Many drivers need to modify settings in SCU and thus need to unlock it
first. This change makes it possible.

Signed-off-by: Maxim Sloyko <maxims@google.com>
Reviewed-by: Simon Glass <sjg@chromium.org>