i#1683 arm disasm: omit implicit writeback args for non-list load/store
i#1683 arm disasm: omit implicit writeback args for non-list load/store

Adds -syntax_arm support for omitting the implicit writeback args for
non-register-list load and store instructions.  Relies on the base
writeback reg always being last.

Does not yet print the "!" after the memory operand as that requires
figuring out whether there is a displacement or not which is non-trivial
and will be done separately.

Review-URL: https://codereview.appspot.com/231040043

daksunt/dynamorio,AmesianX/dynamorio,daksunt/dynamorio,code4bones/dynamorio,code4bones/dynamorio,daksunt/dynamorio,AmesianX/dynamorio,bl4ckic3/dynamorio,AmesianX/dynamorio,code4bones/dynamorio,AmesianX/dynamorio,code4bones/dynamorio,bl4ckic3/dynamorio,bl4ckic3/dynamorio,code4bones/dynamorio,daksunt/dynamorio,AmesianX/dynamorio,bl4ckic3/dynamorio,daksunt/dynamorio,bl4ckic3/dynamorio