Neon: Update mbfilter if all vectors follow one branch.
Change the mbfilter Neon code from executing both branches if all vectors follow only one branch. The code is about 5% faster when executing only one branch and about 1% slower when executing both branches. -PS5: Remove local stack space from mbfilter. Change-Id: I6a23f9b318a9f4568a2718b4c9348db988fe2182