[RISCV] Rename RISCVISD::GREVI(W)/GORCI(W) to RISCVISD::GREV(W)/GORC(W). Don't...

[RISCV] Rename RISCVISD::GREVI(W)/GORCI(W) to RISCVISD::GREV(W)/GORC(W). Don't require second operand to be a constant.

Prep work for adding intrinsics for these instructions in the
future.