Update pack_neon for the new fast ARM32 int8 kernel.
Update pack_neon for the new fast ARM32 int8 kernel.

petewarden/gemmlowp,maciekcc/gemmlowp,petewarden/gemmlowp,google/gemmlowp,google/gemmlowp,petewarden/gemmlowp,maciekcc/gemmlowp,maciekcc/gemmlowp,google/gemmlowp,google/gemmlowp,petewarden/gemmlowp