AVX-512: Implemented DAG lowering for shuff62x2/shufi62x2 instuctions (...

AVX-512: Implemented DAG lowering for shuff62x2/shufi62x2 instuctions ( Shuffle Packed Values at 128-bit Granularity ) 
Tests added , vector-shuffle-512-v8.ll test re-generated.

Differential Revision: http://reviews.llvm.org/D10300

llvm-svn: 239697