Demonstrations for timg as pwm operation.

example code ：
	PA0、PA1、PD12 toggle in timer interrupt 
	TIMG0_CH0 - TIMG0_CH2 PWM 16K
	
1. timer interrupt example：
	fclk：100M。
	cycle：16K
	
	timer cycle calculate：(period+1)/Freq *(Prescaler+1)
	                   = (3124+1)/10000000 * (0+1)
					   =  31.25us
	center mode：cycle = 31.25us *2 = 62.5us
	frequence：1/62.5us = 16000HZ
	



