[RISCV][GlobalISel] Legalize G_ICMP and G_SELECT

Test legalization for (i7, i8, i16, i32, i48, i64) on rv32 and for (i8, i15, i16, i32, i64, i72, i128). Legalization fails for i96 on rv32 and i192 on rv64. Note that [i192 fails for AArch64](https://github.com/llvm/llvm-project/issues/64394).

Reviewed By: craig.topper

Differential Revision: https://reviews.llvm.org/D157023