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,sqrshr$
 and 4 convert instructions:
      scvtf,ucvtf,fcvtzs,fcvtzu


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@189926 91177308-0d34-0410-b5e6-96231b3b80d8