target/riscv: Detect sxl to set bit width for RV32 in RV64

target/riscv: Detect sxl to set bit width for RV32 in RV64

Ensure correct bit width based on sxl when running RV32 on RV64 QEMU.
This is required as MMU address translations run in S-mode.

Signed-off-by: TANG Tiancheng <tangtiancheng.ttc@alibaba-inc.com>
Reviewed-by: Liu Zhiwei <zhiwei_liu@linux.alibaba.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20240919055048.562-5-zhiwei_liu@linux.alibaba.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>