[VE] Add integer arithmetic vector instructions

Add VADD/VADS/VADX/VSUB/VSBS/VSBX/VMPY/VMPS/VMPX/VMPD/VDIV/VDVS/VDVX
instructions.  Also add regression tests.

Reviewed By: simoll

Differential Revision: https://reviews.llvm.org/D89642