[automerger skipped] fsck.f2fs: Split build_segment_manager() to speed up auto-fix am: b5cd946910 -s ours

am skip reason: Change-Id I1dce1039bc01641f7c33875a1cfe20943cdc42ac with SHA-1 31b8f380db is in history

Original change: https://googleplex-android-review.googlesource.com/c/platform/external/f2fs-tools/+/12056203

Change-Id: I4405b0553fcb1d5f6ecce420f6ecd749326c8950