[X86][LLVM]Expanding Supports lowerInterleavedStore() in X86InterleavedAccess (VF8 stride 4):

This patch expands the support of lowerInterleavedStore to 8x8i stride 4.

LLVM creates suboptimal shuffle code-gen for AVX2.
In overall, this patch is a specific fix for the pattern (Strid=4 VF=8) and we plan to include more patterns in the future.

The patch goal is to optimize the following sequence:
At the end of the computation, we have xmm2, xmm0, xmm12 and xmm3 holding
each 8 chars:

c0, c1, , c7
m0, m1, , m7
y0, y1, , y7
k0, k1, ., k7

And these need to be transposed/interleaved and stored like so:

c0 m0 y0 k0 c1 m1 y1 k1 c2 m2 y2 k2 c3 m3 y3 k3 ....

Reviewers
DavidKreitzer
Farhana
zvi
igorb
guyblank
RKSimon
Ayal

Differential Revision: https://reviews.llvm.org/D36058

Change-Id: I3cc5c2ca5d6318901c192a4428493b99ef424c32
llvm-svn: 314109