- scripts/check-kernel-fix: allow explicit git fixes
    - scripts/common-functions:
    
    change -f from flat mode to -f fixes and use -t for the flat mode.
    It seems that the security team is not using the flat mode anyway so we
    might drop it eventually. Let's keep it to play around, it is a trivial
    code anyway.
    
    -f "sha"  now allows to specify explicit Fixes commit shas which would
    extend existing ones.