target/riscv: Remove generate_exception_mtval

target/riscv: Remove generate_exception_mtval

The function doesn't set mtval, it sets badaddr. Move the set
of badaddr directly into gen_exception_inst_addr_mis and use
generate_exception.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20220604231004.49990-3-richard.henderson@linaro.org>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>