[llvm] [RISCV] Enable load clustering by default (PR #73789)

[Philip Reames via llvm-commits]

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

LGTM w/comment addressed.  The comment is basically a rework of the patch, but the resulting patch is near trivial so it felt reasonable to do a conditional LGTM here.  

https://github.com/llvm/llvm-project/pull/73789