For non-retrofit (launch) devices, super.img is used for factory, so
source images should be from target_files.
In this change, build-superimage-target procedure is converted to a
more flexible script so that it can be built.
Bug: 119322123
Test: build target files for device launch with dynamic partitions
Change-Id: I6ee0cc3e145357dfc74be248f81f5f8f4e51fc5c
