powerpc: Enable on demand governor on ppc64_defconfig

This was enabled on the pseries defconfigs recently, but missed
the ppc64 one.
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/configs/ppc64_defconfig

@@ -41,6 +41,7 @@ CONFIG_PPC_CELL_QPACE=y
 CONFIG_RTAS_FLASH=m
 CONFIG_IBMEBUS=y
 CONFIG_CPU_FREQ_PMAC64=y
+CONFIG_CPU_FREQ_DEFAULT_GOV_ONDEMAND=y
 CONFIG_HZ_100=y
 CONFIG_BINFMT_MISC=m
 CONFIG_PPC_TRANSACTIONAL_MEM=y