[RISCV] Match (select C, -1, X)->(or -C, X) during lowerSelect

Same with (select C, X, -1), (select C, 0, X), and (select C, X, 0).

There's a DAGCombine after we turn the select into select_cc, but
that may introduce a setcc that didn't previously exist. We could
add more DAGCombines to remove the extra setcc, but this seemed lower
effort.

Reviewed By: reames

Differential Revision: https://reviews.llvm.org/D135833