AVX-512: Fixed masked load / store instruction selection for KNL.

Patterns were missing for KNL target for <8 x i32>, <8 x float> masked load/store.

This intrinsic comes with all legal types:
<8 x float> @llvm.masked.load.v8f32(<8 x float>* %addr, i32 align, <8 x i1> %mask, <8 x float> %passThru),
but still requires lowering, because VMASKMOVPS, VMASKMOVDQU32 work with 512-bit vectors only.

All data operands should be widened to 512-bit vector.
The mask operand should be widened to v16i1 with zeroes.

Differential Revision: http://reviews.llvm.org/D15265

llvm-svn: 254909