[NFC][LV] Refine the lit test case riscv-vector-reverse.ll (#149020)

This patch includes the following changes:
1. Merge riscv-vector-reverse-output.ll into riscv-vector-reverse.ll,
and only check the generated LLVM IR.
2. Add vplan-riscv-vector-reverse.ll to preserve the original debug
output checks from riscv-vector-reverse.ll.

Author: Mel-Chen