Triangle and Circle DMA drawing functions added

[drvkmr]

Was using them a lot in my sketches, so decided to implement them properly with DMA capabilities.

[Lukaswnd]

Sorry, the code looks nice, but I have to say this:
I think these are GFX functions, they don't belong to the lowest level driver. They belong to the GFX_Lite or the Adafruit_GFX. Or any other gfx you build on top. I simply don't want the lowlevel library to be flooded with higher level GFX stuff, because where do you start and where do you end? what's next a star, pentagon...

But on the otherhand I see that it might be faster if this lib would implement it. The Fill Rect is remarkable faster that the ArduinoGFX version, because it can use hlineDMA

[mrcodetastic]

Thanks for this code @drvkmr. I am not keen on putting this into this library as it's focused on the hardware level only. However, I'll see if I can get it to work from the GFX_Lite library.

We can then perhaps start looking at other cool things that could be put into GFX_Lite as well if I can get this to work.

[drvkmr]

@Lukaswnd @mrcodetastic I understand, will close this PR and we can look at this later for the GFX_Lite library. Have been playing with it already and it looks great!