feature: add support for GPDMA on the DAC peripheral on STM32U5

[RaresAndrei0]

Implemented GPDMA support, tested using a simple u8 transfer to a LED

[RaresAndrei0]

Will improve the function by adding a TriggerTimer enum such that it will become a bit more verbose and easy to use(Typing "Tim6" instead of passing a "5" to the function)

Also will change the DacChannel::new, adding a timer parameter so the GPDMA timer will be declared in the ::new function and will be tied to the DAC instead of declaring and configuring it in main. Should also make the code cleaner and easier to use, this can work for now :)