Allow device/profile owners to update settings.

Device owners can update Settings.Secure and Settings.Global settings.
Profile owners can update Settings.Secure settings.

DMAgent currently needs to live in /system/priv-app in order to
(among other things) update global and secure settings. This change will
get us closer to being able to move DMAgent out of priv-app.
Bug: 14965414

Change-Id: If2cc3a56de91bffde33b838ab8ecea2c32412803