[SLP] Vectorize loads of consecutive memory accesses, accessed in non-consecutive (jumbled) way.

The jumbled scalar loads will be sorted while building the tree and these accesses will be marked to generate shufflevector after the vectorized load with proper mask.

Reviewers: hfinkel, mssimpso, mkuper

Differential Revision: https://reviews.llvm.org/D26905

Change-Id: I9c0c8e6f91a00076a7ee1465440a3f6ae092f7ad
llvm-svn: 293386