[llvm] [RISCV] Convert more constant splats in tests to splat shorthand. NFC (PR #87616)

[Craig Topper via llvm-commits]

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

LGTM assuming no codegen changes are hidden in here. I see you split those out.

https://github.com/llvm/llvm-project/pull/87616