[RISCV] Move Shift Ones instructions from Zbb to Zbp to match 0.93 bitmanip spec.

It's not really clear in the spec that these are in Zbp now, but
that's what I've gather from previous commits to the spec. I've
file an issue to get it documented properly.

Reviewed By: asb, frasercrmck

Differential Revision: https://reviews.llvm.org/D94652