Demonstrations for tim8 as pwm output operation.

example function:
	EBUS event make PWM output pin change other pin
	TIM8_CH0  | PB3
	TIM8_CH0N | PB0 -- change --> PB2
	TIM8_CH1  | PB4 -- change --> PB1 
	TIM8_CH1N | PB1 -- change --> PB0 
	TIM8_CH2  | PB5 -- change --> PA14
	TIM8_CH2N | PB2 -- change --> PA12
	
	
1. PWM output example ：
	FCLK：96M。
	PWM freq：16K
	
	timer cycle calculate formula：(period+1)/Freq *(Prescaler+1)
								= (2999+1)/96000000 * (0+1)
								=  0.00003125s
	centermpde ，cycle*2  = 0.00003125s * 2  = 0.0000625s
				 freq     = 1/0.0000625 = 16000HZ


