arm64: implement
  sshr, ushr, ssra, usra (scalar, imm) 
  srshr, urshr, srsra, ursra (scalar, imm) 
  srshr, urshr, srsra, ursra (vector, imm) 
  sshl, srshl, ushl, urshl (scalar, imm) 
  sshl, srshl, ushl, urshl (vector, vector) 
  ssra, usra (vector, imm) 


git-svn-id: svn://svn.valgrind.org/vex@2926 8f6e269a-dfd6-0310-a8e1-e2731360e62c
arm64: implement srhadd, urhadd (vector)


git-svn-id: svn://svn.valgrind.org/vex@2927 8f6e269a-dfd6-0310-a8e1-e2731360e62c