Generate care_map.txt when AVB is enabled

When AVB is enabled, generate care_map.txt and add it to the target
files. Also copy it into the OTA package where it will later be used
by the update_verifier.

Bug: 62208947
Test: \
1. Run add_img_to_target_files on the TF of a new pixel device,
and care_map.txt generates successfully.

2. Make dist in oc-dr1-release and find care_map.txt in the OTA package.

3. update_verifier succeeds in reading all the blocks on the care_map,
and fails to read out-of-bound blocks.

Change-Id: I2881711e6f87789cb7de150dbeca18b756fed68a