A64: Let the Simulator trap BLR XZR instructions.

This instruction is used as a guard for the constant pool.

R=ulan@chromium.org

Review URL: https://codereview.chromium.org/170673003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19461 ce2b1a6d-e550-0410-aec6-3dcde31c8c00