Refactor the ARM target parsing to use a def file with macros to expand

the necessary tables.

This will allow me to restructure the code and structures using this to
be significantly more efficient. It also removes the duplication of the
list of several enumerators. It also enshrines that the order of
enumerators match the order of the entries in the tables, something the
implementation code actually uses.

No functionality changed (yet).

llvm-svn: 246370