[Hexagon] Resubmission of 220427
Modified library structure to deal with circular dependency between HexagonInstPrinter and HexagonMCInst.
Adding encoding bits for add opcode.
Adding llvm-mc tests.
Removing unit tests.

http://reviews.llvm.org/D5624

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@220584 91177308-0d34-0410-b5e6-96231b3b80d8