Adds vabs instruction to simulator, assembler, disassembler and tests.

BUG=none
TEST=Added to cctest.

Review URL: http://codereview.chromium.org/6366016

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6531 ce2b1a6d-e550-0410-aec6-3dcde31c8c00