linux: enable CONFIG_CPU_IDLE

Signed-off-by: Stewart Smith <stewart@linux.vnet.ibm.com>
diff --git a/openpower/configs/linux/skiroot_defconfig b/openpower/configs/linux/skiroot_defconfig
index 4f6c885..e2db681 100644
--- a/openpower/configs/linux/skiroot_defconfig
+++ b/openpower/configs/linux/skiroot_defconfig
@@ -36,6 +36,7 @@
 # CONFIG_IOSCHED_DEADLINE is not set
 # CONFIG_PPC_PSERIES is not set
 CONFIG_CPU_FREQ_DEFAULT_GOV_ONDEMAND=y
+CONFIG_CPU_IDLE=y
 CONFIG_HZ_100=y
 CONFIG_KEXEC=y
 CONFIG_IRQ_ALL_CPUS=y