Convert getMemIntrinsicNode to take ArrayRef of SDValue instead of pointer and size.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207329 91177308-0d34-0410-b5e6-96231b3b80d8
Replace std::vector with SmallVector for some small, known size vectors.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207330 91177308-0d34-0410-b5e6-96231b3b80d8