Add TLI.allowsMisalignedMemoryAccesses to LoadStoreVectorizer

Summary: Extend TTI to access TLI.allowsMisalignedMemoryAccesses(). Check condition when vectorizing load and store chains.
Add additional parameters: AddressSpace, Alignment, Fast.

Reviewers: llvm-commits, jlebar

Subscribers: arsenm, mzolotukhin

Differential Revision: http://reviews.llvm.org/D21935

llvm-svn: 275100