[VE] Add vector float instructions

Add VFAD/VFSB/VFMP/VFDV/VFSQRT/VFCP/VFCM/VFMAD/VFMSB/VFNMAD/VFNMSB/
VRCP/VRSQRT/VRSQRTNEX/VFIX/VFIXX/VFLT/VFLTX/VCVS/VCVD instructions.
Add regression tests too.  Also add additional AsmParser for VFIX
and VFIXX instructions to parse their mnemonic.

Reviewed By: simoll

Differential Revision: https://reviews.llvm.org/D90166