Implement ARM SDIV and UDIV instructions.  Fixes #314178.  Partially
based on a patch by Ben Cheng, bccheng@android.com.  Also renames two
misnamed PPC helpers.


git-svn-id: svn://svn.valgrind.org/vex/trunk@2706 8f6e269a-dfd6-0310-a8e1-e2731360e62c