arm64: implement: sqneg, {u,s}q{add,sub} (scalar),
{sqdmlal,sqdmlsl,sqdmull} (vector x element)

As part of this, rename Iop_QDMulLong* to Iop_QDMull* so as to be
consistent with their non-saturating equivalents.



git-svn-id: svn://svn.valgrind.org/vex/trunk@2907 8f6e269a-dfd6-0310-a8e1-e2731360e62c