CH32V103 Support

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the CH32V103 is the cheapest 5V MCU i know with a USB host/device controller. so it would be amazing if tinyUSB supported it. it's similar to the CH32V20x/307, but there are some slight differences with the USB controller.

i briefly tried myself at adding host support for it a while ago, but ran into some issues.
specifically i didn't realize that the 20x/307 ports only implement the device API, not the host API (which is the one i wanted). plus i wasn't able to write the host API port from scratch either because there appears to be no documentation on it (the porting guide only explains the device API)

so beyond having a port, some updated documentation would also be nice...