Update the timeout list dialog in display and security settings.

Currently, we add padlocks to all the timeout options which are
more than the timeout enforced by the admin. Instead of adding
the padlocks to the options, updated the timeout list dialog to
have a disabled by admin message as dialog footer.

Bug: 27564363
Change-Id: I66ce35e92c044ce1864d14e1fc0e83881f8f4ab0