[PATCH] [ARM64]Fix the bug cannot select UQSHL/SQSHL with constant i64 shift amount.

[Hao Liu]

Hi Tim,

After added LLVM CodeGen test, these patches have been committed in http://llvm.org/viewvc/llvm-project?rev=207399&view=rev  and and http://llvm.org/viewvc/llvm-project?rev=207401&view=rev.

Thanks,
-Hao

http://reviews.llvm.org/D3501