ARM IAS: fix after r198172

The DPR and SPR register lists are also register lists.  Furthermore, the
registers need not be checked individually since the register type can be
checked via the list kind.  Use that to simplify the logic and fix the incorrect
assertion.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198174 91177308-0d34-0410-b5e6-96231b3b80d8