target/riscv: rvv-1.0: add mstatus VS field

target/riscv: rvv-1.0: add mstatus VS field

Signed-off-by: LIU Zhiwei <zhiwei_liu@c-sky.com>
Signed-off-by: Frank Chang <frank.chang@sifive.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20211210075704.23951-4-frank.chang@sifive.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>