Implemented DMA support for PWM

[python36]

1. Changed the calculation of Compare_Value to avoid variable overflow after the first multiplication.
2. The Compare_Value calculation has been moved to a separate Calculate_Compare_Value function to allow this function to be used to calculate DMA array values.
3. Created Data_Register_Address function to get the timer register address for use in DMA.
4. Created demo_pwm_dma_continuous example to demonstrate usage of DMA for PWM. Realized smooth blink on STM32F4XX board.