[VPlan] VPlan version of InterleavedAccessInfo.

This patch turns InterleaveGroup into a template with the instruction type
being a template parameter. It also adds a VPInterleavedAccessInfo class, which
only contains a mapping from VPInstructions to their respective InterleaveGroup.
As we do not have access to scalar evolution in VPlan, we can re-use
convert InterleavedAccessInfo to VPInterleavedAccess info.


Reviewers: Ayal, mssimpso, hfinkel, dcaballe, rengolin, mkuper, hsaito

Reviewed By: rengolin

Differential Revision: https://reviews.llvm.org/D49489

llvm-svn: 346758