target/riscv: Convert the RISC-V exceptions to an enum

Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: f191dcf08bf413a822e743a7c7f824d68879a527.1617290165.git.alistair.francis@wdc.com
3 files changed