Use TableGen'erated pseudo lowering for ARM.

Use TableGen'erated pseudo lowering for ARM.

Hook up the TableGen lowering for simple pseudo instructions for ARM and
use it for a subset of the many pseudos the backend has as proof of concept.

More conversions to come.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@134705 91177308-0d34-0410-b5e6-96231b3b80d8