pixel-sepolicy: init_dpm.sh to read/write on custom_ab_block_device am: e682a521ee am: c1749ffce7

Original change: https://googleplex-android-review.googlesource.com/c/platform/hardware/google/pixel-sepolicy/+/23469768

Change-Id: I3e3fe05b915270a8dc8e8e002c4ace4c2ba78aec
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>