kmod.prov: fix and speed it up
    
    For kernel builds, /usr/lib/rpm/kmod.prov is fork+execed by rpmbuild
    in "Processing files:" step about 8000 times, single-threaded,
    with cumulative run time of ~2 minutes.
    
    Speed up this script, by avoiding additional fork+execing.
    
    Tested to work, observed speedup: almost exactly 2 times faster.
    
    While verifying correctness, noticed that old script was buggy -
    it was generating a bogus "Provides:" item - kmod(modules.builtin.modinfo),
    because the logic in script was filtering for */*.ko files and
    for */modules.builtin* files, and wasn't prepared for
    the existence of */modules.builtin.modinfo file.
    
    Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>