target/riscv: Use gen_arith_per_ol for RVM

target/riscv: Use gen_arith_per_ol for RVM

The multiply high-part instructions require a separate
implementation for RV32 when TARGET_LONG_BITS == 64.

Reviewed-by: LIU Zhiwei <zhiwei_liu@c-sky.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20211020031709.359469-11-richard.henderson@linaro.org
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>