avr_timer: rework timer comparator cycle timers.

timer comparator handlers have been reworked to use pointer to
 comparator structure as parameter from cycle timer.  as part, all
 timer cancel operations have changed to single function to handle
 the cancel of timers based on pointer to comparator structure as
 parameter.

	modified:   ../../simavr/sim/avr_timer.c
	modified:   ../../simavr/sim/avr_timer.h