[RISCV] Add integer min/max intrinsic tests. NFC

Add basic tests and some tests for same operands and all undef
operands inspired by PR55271.

i32 is umin/umax is using signext to match RISC-V ABI. i8/i16 are
using signext/zeroext to match the operation.

Differential Revision: https://reviews.llvm.org/D124948