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

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

The handler methods for divw[u] instructions internally use Rc(ctx->opcode),
for extraction of Rc field of instructions, which poses a problem if we move
the above said instructions to decodetree, as the ctx->opcode field is not
popluated in decodetree. Hence, making it decodetree compatible, so that the
mentioned insns can be safely move to decodetree specs.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Chinmay Rath <rathc@linux.ibm.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>