target/ppc: Make divd[u] handler method decodetree compatible

target/ppc: Make divd[u] handler method decodetree compatible

This is like commit 86e6202a57b1 ("target/ppc: Make divw[u] handler
method decodetree compatible."), but for gen_op_arith_divd().

Cc: qemu-stable@nongnu.org
Suggested-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>