pid1: parse CPUAffinity= in incremental fashion
    
    This makes the handling of this option match what we do in unit files. I think
    consistency is important here. (As it happens, it is the only option in
    system.conf that is "non-atomic", i.e. where there's a list of things which can
    be split over multiple assignments. All other options are single-valued, so
    there's no issue of how to handle multiple assignments.)
    
    (cherry picked from commit 61fbbac1d517a0b3498a689c736c6ca918497904)
    
    Related: #1734787
    
    patch_name: 0276-pid1-parse-CPUAffinity-in-incremental-fashion.patch
    present_in_specfile: true
    location_in_specfile: 276
    squash_commits: true