Support SD card encryption when possible

* We support SD card encryption when:
  1) We support device encryption and
  2) There are no removable volumes
* We use a private API in StorageManager to walk through mounted and
  unmounted volumes to determine whether any are removable

Bug: 5794891

Change-Id: I514828dd53604b9d495d0838dd24ed1f28d61c06
1 file changed