Generate chd_merged_sepolicy while building CHD am: 9385a0ee82 am: e8b9dee2e4 am: 651766b570

Original change: https://android-review.googlesource.com/c/platform/tools/treble/+/2895000

Change-Id: Ia0fdd2ef63f5a4ce8259c0b3b5a46582e0749ef6
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>