arm64: implement: sadalp uadalp saddlp uaddlp saddlv uaddlv saddw{2}
uaddw{2} ssubw{2} usubw{2} shadd uhadd shsub uhsub sqadd uqadd sqsub
uqsub smaxp umaxp sminp uminp



git-svn-id: svn://svn.valgrind.org/vex/trunk@2895 8f6e269a-dfd6-0310-a8e1-e2731360e62c