ANDROID: dm-bow: Add block_size option

Also consolidated changes to limits, including no longer changing
underlying device.

Bug: 153512828
Test: device boots, checkpoints can be committed or rolled back with and
without this parameter, parameter is accepted
Change-Id: I6fcb9bc21353a16ae0bf8998ffa22094eb1cbf3a
Signed-off-by: Paul Lawrence <paullawrence@google.com>
(cherry picked from commit 7df64f62)