Arm64 compiles "x +_64 (y >> shift)" into a single instruction if
"shift" is a constant. The code generator expects that "shift" is a
32 bit constant. however, TurboFan can also pass in a 64 bit constant,
which caused a crash in the code generator.

With this CL we cast the constant of TurboFan to an int in the
instruction selector and thereby satisfy the assumption of the code
generator. This should be correct since the code generator anyways cast
the "shift" to an int5 or int6 eventually.

R=v8-arm-ports@googlegroups.com
BUG=v8:5923

Review-Url: https://codereview.chromium.org/2669203005
Cr-Commit-Position: refs/heads/master@{#43036}