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

[Pengcheng Wang via llvm-commits]

wangpc-pp wrote:

> I've rebased and repushed (again actually, I had done it before but forgotten to push). I've adopted Philip's suggestion of just flipping the default for the option for this patch.

Thanks! It seems there are new conflicts (we are actively changing).
I found some regressions, but I don't mean to block this patch.

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