[X86] Use PreprocessISelDAG to convert vector sra/srl/shl to the X86 specific variabl...

[X86] Use PreprocessISelDAG to convert vector sra/srl/shl to the X86 specific variable shift ISD opcodes.

These allows use to use the same set of isel patterns for sra/srl/shl which are undefined for out of range shifts and intrinsic shifts which aren't undefined.

Doing this late allows DAG combine to have every opportunity to optimize the sra/srl/shl nodes.

This removes about 7000 bytes from the isel table and simplies the td files.

llvm-svn: 355071