Inplement aarch64 neon instructions in AdvSIMD(shift). About 24 shift instructions:
      sshr,ushr,ssra,usra,srshr,urshr,srsra,ursra,sri,shl,sli,sqshlu,sqshl,uqshl,shrn,sqrshrun,sqshrn,uqshr,sqrshrn,uqrshrn,sshll,ushll
 and 4 convert instructions:
      scvtf,ucvtf,fcvtzs,fcvtzu


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@189925 91177308-0d34-0410-b5e6-96231b3b80d8