[llvm] [RISCV][GISel] Use boolean predicated legalization action methods to simplify code. NFC (PR #115063)

[Sam Elliott via llvm-commits]

lenary wrote:

Is there any value in our backend having a test like `llvm/test/CodeGen/AArch64/GlobalISel/legalizer-info-validation.mir`? If we think so, we're probably going to need one for each feature combination used in these predicates. 

https://github.com/llvm/llvm-project/pull/115063