target/riscv: Set env->bins in gen_exception_illegal

target/riscv: Set env->bins in gen_exception_illegal

While we set env->bins when unwinding for ILLEGAL_INST,
from e.g. csrrw, we weren't setting it for immediately
illegal instructions.

Add a testcase for mtval via both exception paths.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1060
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20220604231004.49990-2-richard.henderson@linaro.org>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>