Avoid using alarm APIs for LPM when Idle timeout is zero

Avoid using alarm APIs for LPM when Idle timeout is zero

For some vendors the idle timer value is configured to zero. But with
the current LPM timer implementation it will use the alarm APIs to
schedule wake_deassert(), which introduces context switch overhead.
The code is modified to trigger the wake_deassert immediately if the
idle timeout value is configured to zero. These changes improve OPP
throughput.

Change-Id: Ic48e7b990ccf55525a0d15b65c03daedfe03c582
Signed-off-by: Jaganath Kanakkassery <jaganathx.kanakkassery@intel.com>
Signed-off-by: Zhiquan Liu <zhiquan.liu@intel.com>