tests: kernel: add tickless test

Added test cases to verify tickless idle concepts defined in
https://www.zephyrproject.org/doc/subsystems/power_management.html#tickless-idle



Test points:
verify system clock recovery after exiting tickless idle;
verify slicing scheduler behaves as expected

Jira: ZEP-339

Change-Id: Ic0a86d725e9692aa217375cedc7396372a026a88
Signed-off-by: Sharron LIU <sharron.liu@intel.com>