arm64: implement: {sli,sri} (vector & scalar), sqabs (vector & scalar)

Fix instruction decoding bug in dis_AdvSIMD_vector_x_indexed_elem
introduced in r2874 but not exposed until recently.



git-svn-id: svn://svn.valgrind.org/vex@2899 8f6e269a-dfd6-0310-a8e1-e2731360e62c