[RISCV] Add a Zbb+Zbs command line to rv*zbs.ll to get coverage on an existing isel pattern. NFC

This pattern wasn't tested

def : Pat<(XLenVT (and (rotl -2, (XLenVT GPR:$rs2)), GPR:$rs1)),
          (BCLR GPR:$rs1, GPR:$rs2)>;1