[X86] Call lowerShuffleAsBitMask for 512-bit vectors in lowerShuffleAsBlend.

[X86] Call lowerShuffleAsBitMask for 512-bit vectors in lowerShuffleAsBlend.

This patch enables the use of lowerShuffleAsBitMask for 512-bit blends before
falling back to move immedate, GPR to k-register, and masked op.

I had to make some changes to support v8i64 when i64 is not a legal type. And to
support floating point types.

This trades a load for the move immediate and GPR move which is higher latency.
But its probably better for register pressure not having to hop through other
register classes. The load+and should play better with LICM and
rematerialization I think.

Differential Revision: https://reviews.llvm.org/D59479

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@356618 91177308-0d34-0410-b5e6-96231b3b80d8