[X86][LLVM]Expanding Supports lowerInterleavedLoad() in X86InterleavedAccess...

[X86][LLVM]Expanding Supports lowerInterleavedLoad() in X86InterleavedAccess (VF{8|16|32} stride 3).

This patch expands the support of lowerInterleavedload to {8|16|32}x8i stride 3.

LLVM creates suboptimal shuffle code-gen for AVX2. In overall, this patch is a specific fix for the pattern (Strid=3 VF={8|16|32}) and we plan to include the store (deinterleved side).

The patch goal is to optimize the following sequence:
a0 b0 c0 a1 b1 c1 a2 b2
c2 a3 b3 c3 a4 b4 c4 a5
b5 c5 a6 b6 c6 a7 b7 c7

into

a0 a1 a2 a3 a4 a5 a6 a7
b0 b1 b2 b3 b4 b5 b6 b7
c0 c1 c2 c3 c4 c5 c6 c7

Reviewers
1. zvi
2. igor
3. guyblank
4. dorit
5. Ayal

llvm-svn: 312722