target/ppc: Remove xscmpnedp instruction

xscmpnedp was added in ISA v3.0 but removed in v3.0B. This patch
removes this instruction as it was not in the final version of v3.0.

Signed-off-by: Víctor Colombo <victor.colombo@eldorado.org.br>
Acked-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Matheus Ferst <matheus.ferst@eldorado.org.br>
Message-Id: <20220225210936.1749575-40-matheus.ferst@eldorado.org.br>
Signed-off-by: Cédric Le Goater <clg@kaod.org>