Revert "ANDROID: dm-bow: remove dm-bow"

This reverts commit dc855f8b.

Support for ext4 for userdata has been restored, so we must also restore
dm-bow

Note that since it was deprecated, a few things have changed at the dm
layer, so there are follow-on patches to fix up all the issues

aosp/3238494 enables checkpoints on ext4 in cuttlefish, get this too

With all the patches in place, run:

launch_cvd \
  -userdata_format="ext4" \
  --data_policy=always_create --blank_data_image_mb=16000

then run

atest vts_kernel_checkpoint_test

Test: atest vts_kernel_checkpoint_test passes
Bug: 210958368
Bug: 379587919
Change-Id: I06ad3c7870b67080dfd6d72917751b20193a4fd6
Signed-off-by: Paul Lawrence <paullawrence@google.com>