target/riscv: Extract virt enabled state from tb flags

target/riscv: Extract virt enabled state from tb flags

Virt enabled state is not a constant, so we should put it into tb flags.
Thus we can use it like a constant condition at translation phase.

Reported-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com>
Reviewed-by: Weiwei Li <liweiwei@iscas.ac.cn>
Message-Id: <20230324143031.1093-2-zhiwei_liu@linux.alibaba.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Tested-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Message-Id: <20230325105429.1142530-2-richard.henderson@linaro.org>
Message-Id: <20230412114333.118895-2-richard.henderson@linaro.org>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>