Add BOARD_SUPER_IMAGE_IN_UPDATE_PACKAGE flag.

When set, product-img-tag.zip contains super.img instead of individual
user images from target files. For virtual devices, super.img is needed
to boot the device, but individual user images aren't needed.

Test: on A/B DAP, with flag set:
     - m updatepackage and look at img.zip
     - img_from_target_files
     both have super.img and not system / vendor / system_other
Test: on non-A/B DAP, with the flag set:
     - m updatepackage and look at img.zip
     - img_from_target_files
     both have super.img and not system / vendor
Test: on A/B retrofit, with the flag set:
     - m updatepackage and look at img.zip
     - img_from_target_files
     both have super_*.img and system_other.img, but not system / vendor
Bug: 113175337

Change-Id: I94e33091d0c837cae40776176b4dcfdd338aba90