This commit constructs the super_vbmeta image to eliminate the
need of adding /vbmeta_system and/or /vbmeta_vendor when AVB
chain partition is used with Android Dynamic Partition.
See BOARD_AVB_VBMETA_SYSTEM under the link:
https://android.googlesource.com/platform/external/avb/#build-system-integration
The structure of super_vbmeta :
| VBMeta Table | (fixed-length 2KiB)
| Backup VBMeta Table | (fixed-length 2KiB)
| VBMeta Images | (fixed-length 64KiB each)
The structure of VBMeta Table :
| Super VBMeta Header | (fixed-length 128B)
| VBMeta Descriptors | (variable-length)
The VBMeta Table records the slot number of each
vbmeta image within the /super_vbmeta partition.
Bug: 137054296
Test: m libvbmeta_test
Test: ./out/host/linux-x86/nativetest/libvbmeta_test/libvbmeta_test
Change-Id: I01aeadd850750ae87d9125484c1b1f570bb84756
