lpm-levels: Select lpm for isolated cpu when sleep is disabled

Isolated cpu can enter to wfi if sleep is disabled and stay in
wfi until it wakes up and selects deeper lpm again.

Select cpu lpm for isolated cpu when sleep is disabled.

Change-Id: Id936ebaac0118d48d07e74aff7569f93b8b98b8b
Signed-off-by: Maulik Shah <mkshah@codeaurora.org>