armv6: Add over_n_8888 fast path (disabled)

armv6: Add over_n_8888 fast path (disabled)

This new fast path is initially disabled by putting the entries in the
lookup table after the sentinel. The compiler cannot tell the new code
is not used, so it cannot eliminate the code. Also the lookup table size
will include the new fast path. When the follow-up patch then enables
the new fast path, the binary layout (alignments, size, etc.) will stay
the same compared to the disabled case.

Keeping the binary layout identical is important for benchmarking on
Raspberry Pi 1. The addresses at which functions are loaded will have a
significant impact on benchmark results, causing unexpected performance
changes. Keeping all function addresses the same across the patch
enabling a new fast path improves the reliability of benchmarks.

Benchmark results are included in the patch enabling this fast path.

[Pekka: disabled the fast path, commit message]
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>