[llvm] [RISCV] Combine 3 bit-manip extensions into `B` (PR #132858)

[Craig Topper via llvm-commits]

https://github.com/topperc approved this pull request.

LGTM

My only concern is that this will break what versions of binutils we can use with -fno-integrated-as. But I'm tired of raising this on every patch like this were an older extension name needs to imply a newer extension name. So I'm going to stop.

https://github.com/llvm/llvm-project/pull/132858