target/riscv: Set opcode to env->bins for illegal/virtual instruction fault

target/riscv: Set opcode to env->bins for illegal/virtual instruction fault

decode_save_opc() will not work for generate_exception(), since 0 is passed
to riscv_raise_exception() as pc in helper_raise_exception(), and bins will
not be restored in this case.

Signed-off-by: Weiwei Li <liweiwei@iscas.ac.cn>
Signed-off-by: Junqiang Wang <wangjunqiang@iscas.ac.cn>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20230330034636.44585-1-liweiwei@iscas.ac.cn>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>