samples: power: Time is passed as milliseconds in tickless kernel

In tickless kernel mode, time parameter of _sys_soc_suspend is in
milliseconds. Based on the kernel mode use the correct
mulitplier to convert to seconds.

Jira:1821
Change-Id: Idf156f56ece79a82729ebb124d1552a5eeb69e25
Signed-off-by: Ramesh Thomas <ramesh.thomas@intel.com>