sched: core: added ifdefs for event mutexes.

Added ifdefs around event mutex specific code. Temporarily disabled the
these same ifdefs (CONFIG_EVENT_MUTEX) in the mutex header, has the
mutexes are far from ready to use. The standard mutexes should be used
untill they are the event based ones are mainlined.

Signed-off-by: Michel Megens <dev@michelmegens.net>