[Hexagon] Add support for getRegisterByName.

Support required to build the Hexagon Linux kernel.

Differential Revision: https://reviews.llvm.org/D51363

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@341238 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed