i#1844: fix drreg assert on aflags preservation on ARM
i#1844: fix drreg assert on aflags preservation on ARM

Relaxes a drreg assert that fires when aflags are spilled and restored with
different registers, which is perfectly legal.

Fixes #1844

Review-URL: https://codereview.appspot.com/282150043

AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio