[Power9] Implement new vsx instructions: quad-precision move, fp-arithmetic

This change implements the following vsx instructions:

- quad-precision move
    xscpsgnqp, xsabsqp, xsnegqp, xsnabsqp

- quad-precision fp-arithmetic
    xsaddqp(o) xsdivqp(o) xsmulqp(o) xssqrtqp(o) xssubqp(o)
    xsmaddqp(o) xsmsubqp(o) xsnmaddqp(o) xsnmsubqp(o)

22 instructions

Thanks Nemanja and Kit for careful review and invaluable discussion!
Reviewers: hal, nemanja, kbarton, tjablin, amehsan

http://reviews.llvm.org/D16110

llvm-svn: 264565