target/riscv: Fix the mstatus.MPP value after executing MRET

The MPP will be set to the least-privileged supported mode (U if
U-mode is implemented, else M).

Signed-off-by: Weiwei Li <liweiwei@iscas.ac.cn>
Signed-off-by: Junqiang Wang <wangjunqiang@iscas.ac.cn>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20230407014743.18779-2-liweiwei@iscas.ac.cn>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
1 file changed