[Target] Teach the query interfaces for lowering of extloads and
truncstores to support EVTs and return expand for non-simple ones.

This makes them more consistent with the isLegal... query style methods
and makes using them simpler in many scenarios.

No functionality actually changed.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213860 91177308-0d34-0410-b5e6-96231b3b80d8