[Power9] Implement new altivec instructions: permute, count zero, extend sign,...

[Power9] Implement new altivec instructions: permute, count zero, extend sign, negate, parity, shift/rotate, mul10

This change implements the following vector operations:
- vclzlsbb vctzlsbb vctzb vctzd vctzh vctzw
- vextsb2w vextsh2w vextsb2d vextsh2d vextsw2d
- vnegd vnegw
- vprtybd vprtybq vprtybw
- vbpermd vpermr
- vrlwnm vrlwmi vrldnm vrldmi vslv vsrv
- vmul10cuq vmul10uq vmul10ecuq vmul10euq

28 instructions

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

Phabricator: http://reviews.llvm.org/D15887
llvm-svn: 264504