target/riscv: Use xl instead of mxl for disassemble

target/riscv: Use xl instead of mxl for disassemble

Disassemble function(plugin_disas, target_disas, monitor_disas) will
always call set_disas_info before disassembling instructions.

plugin_disas  and target_disas will always be called under a TB, which
has the same XLEN.

We can't ensure that monitor_disas will always be called under a TB,
but current XLEN will still be a better choice, thus we can ensure at
least the disassemble of the nearest one TB is right.

Signed-off-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Christoph Müllner <christoph.muellner@vrull.eu>
Message-Id: <20230612111034.3955227-2-christoph.muellner@vrull.eu>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>