drivers: cpuidle: lpm-levels: Reset suspend wake time

During suspend alarm timer sends next wakeup time to
be programmed. Currently next wakeup time is not reset
upon wakeup. This causes unintended wakeups if there is
no alarm set during next suspend.

Reset suspend wake time during exit from suspend.

Change-Id: Ia0e5d08a4e5cdc71f6c2d884363b830de5ef88d5
Signed-off-by: Maulik Shah <mkshah@codeaurora.org>