Implement a few more vector aarch64 insns:

Implement a few more vector aarch64 insns:
LD1 {vT.8h}, [xN|SP], #16
LD1 {vT.16b}, [xN|SP], #16
ST1 {vT.4h}, [xN|SP], #8
MUL  Vd.T, Vn.T, Vm.T
PMUL Vd.T, Vn.T, Vm.T  (fe only)
MLA  Vd.T, Vn.T, Vm.T
MLS  Vd.T, Vn.T, Vm.T
UMOV Xd/Wd, Vn.Ts[index]
SMOV Xd/Wd, Vn.Ts[index]

git-svn-id: svn://svn.valgrind.org/vex/trunk@2813