powerpc: Don't build powernv for other platform defconfigs

Because powernv arrived after these other platforms, the defconfigs
didn't have PPC_POWERNV disabled, and being default y it gets turned on.

If we're going to bother having defconfigs for the specific platforms
then they should only build the code required for those platforms.

The grab bag of everything config is ppc64_defconfig.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
diff --git a/arch/powerpc/configs/cell_defconfig b/arch/powerpc/configs/cell_defconfig
index 45fd06c..7a7b3c8 100644
--- a/arch/powerpc/configs/cell_defconfig
+++ b/arch/powerpc/configs/cell_defconfig
@@ -18,6 +18,7 @@
 CONFIG_MODULES=y
 CONFIG_MODULE_UNLOAD=y
 # CONFIG_BLK_DEV_BSG is not set
+# CONFIG_PPC_POWERNV is not set
 # CONFIG_PPC_PSERIES is not set
 # CONFIG_PPC_PMAC is not set
 CONFIG_PPC_PS3=y