INT 15,C3 - Enable/Disable Watchdog Timer (PS/2)

	AH = C3
	AL = 0	disable watchdog time-out
	   = 1	enable watchdog time-out
	BX = watchdog timer count (1-255)

	on return:
	CF = 0 if successful
	   = 1 if error
	AH = when CF set, 80h for PC & PCjr, 86h for XT, AT & Model 30


	- the watchdog timer is available only on PS/2 with 80286 and
	  80386 processors.
	- the timer uses channel timer channel 3 and IRQ0.  Activated
	  when IRQ0 is active for more than one channel 0 timer cycle,
	  which causes the timer to be decremented.   When the watch-
	  dog timer reaches 0, and NMI is generated.