Improve support for vmrs/vmsr in ARM disassembler.  This is a commit of http://codereview.chromium.org/4904001 for Martyn Capewell.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@5824 ce2b1a6d-e550-0410-aec6-3dcde31c8c00