arm64: enable test cases for
  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/valgrind/trunk@14300 a5019735-40e9-0310-863c-91ae7b9d1cf9