powerpc/85xx: use one kernel option for all the CoreNet_Generic boards

Currently all these boards use the same machine struct and also select
the same kernel options, so it seems a bit of redundant to keep one
separate kernel option for each board. Also update the defconfigs
according to this change.

Signed-off-by: Kevin Hao <haokexin@gmail.com>
Signed-off-by: Scott Wood <scottwood@freescale.com>
diff --git a/arch/powerpc/configs/ppc64e_defconfig b/arch/powerpc/configs/ppc64e_defconfig
index 0085dc4..0a6be6d 100644
--- a/arch/powerpc/configs/ppc64e_defconfig
+++ b/arch/powerpc/configs/ppc64e_defconfig
@@ -23,7 +23,7 @@
 CONFIG_PARTITION_ADVANCED=y
 CONFIG_MAC_PARTITION=y
 CONFIG_EFI_PARTITION=y
-CONFIG_P5020_DS=y
+CONFIG_CORENET_GENERIC=y
 CONFIG_CPU_FREQ=y
 CONFIG_CPU_FREQ_GOV_POWERSAVE=y
 CONFIG_CPU_FREQ_GOV_USERSPACE=y