[llvm] [RISCV] Only convert volatile i64 load/store to Zilsd in SelectionDAG. (PR #169529)

[Sam Elliott via llvm-commits]

lenary wrote:

I had a thought at lunch, which might be helpful.

What if we codegen the non-volatile loads/stores to `PseudoLD_RV32_OPT`/`PseudoSD_RV32_OPT` - this does the "keep things together as long as possible", but also allows the compiler to split them later if needed. Would this make any sense?

https://github.com/llvm/llvm-project/pull/169529