Allow addition of recovery DTBO to recovery image

Non-A/B devices need to include the DTBO image
within the recovery partition to be self-sufficient
and prevent OTA failures.

Test: Ran 'm dist' and verified that the DTBO image
was included in recovery.img using unpack_bootimg.
Also ran 'make' and verified that the DTBO image was
included in recovery.img using unpack_bootimg.
Also tested that aosp_angler-userdebug could
boot into recovery(including a fake dtbo.img
in recovery image).

Bug: 74763691

Change-Id: I38c9c395c95d21f4da42cfa646063bd4416f6bd8