cpuidle: lpm-levels: no hotplug for single core

Register for hotplug and dev_pm_qos notification only
for SMP so covering under CONFIG_SMP flag.

Change-Id: Ic3da9648a4dd5c762cd97dbb9f1915f79bd2481e
Signed-off-by: Lina Iyer <ilina@codeaurora.org>
Signed-off-by: Tushar Nimkar <tnimkar@codeaurora.org>