[X86] Autoupgrade kunpck intrinsics using vector operations instead of scalar operations

Summary: This patch changes the kunpck intrinsic autoupgrade to use vXi1 shufflevector operations to perform vector extracts and concats. This more closely matches the definition of the kunpck instructions. Currently we rely on a DAG combine to turn the scalar shift/and/or code into a concat vectors operation. By doing it in the IR we get this for free.

Reviewers: spatel, RKSimon, zvi, jina.nahias

Reviewed By: RKSimon

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D42018

llvm-svn: 322462