Update accessibility to be encryption-aware.

Look for both EA and non-EA accessibility services, but when the user
is locked only bind to EA services.  Once the user is unlocked, we
take another pass and bind to any non-EA services.

We only consider disabling accessibility once the user is unlocked,
since there could be non-EA services waiting in the wings.

Bug: 25860579
Change-Id: I97bd019661457c3577d629ba12290d02f026011a