[llvm] [AArch64][SVE] Fold ADD+CNTB to INCB and DECB (PR #118280)

[Paul Walker via llvm-commits]

https://github.com/paulwalker-arm approved this pull request.

Looks good to me. Although it does remind me to revisit the add/sub vscale work to see if there's a better way to capture all the requirements but using less patterns.  The need to handle 64-bit and 32-bit separately still irks me.

https://github.com/llvm/llvm-project/pull/118280