target/riscv: Add check for supported privilege mode combinations
There are 3 suggested privilege mode combinations listed in section 1.2
of the riscv-privileged spec(draft-
20220717):
1) M, 2) M, U 3) M, S, U
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>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Message-Id: <
20220718130955.11899-2-liweiwei@iscas.ac.cn>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>