timing: introduce timing functions as a generic feature

Add timing functions and APIs.  This is now used with some of the tests
we have for performance and metrics and will be used whereever timing
informations are needed, for example for tracing, profiling and other
operations where timing info is critical.

Signed-off-by: Daniel Leung <daniel.leung@intel.com>
Signed-off-by: Anas Nashif <anas.nashif@intel.com>