[AVR] Add AVRISelDAGToDAG.cpp

Summary: This pulls the AVR instruction selector in-tree.

Reviewers: arsenm, kparzysz

Subscribers: llvm-commits, wdng, beanz, japaric, mgorny

Differential Revision: https://reviews.llvm.org/D25278

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@285270 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed