(Suggestion) Add function for configuring pullup/down on inputs

[jglim]

Hello!

While interfacing the ch32v003 with a rotary encoder, I could not find a quick and "easy" way to configure the input pins as pullups, so I wrote this snippet:

#define FUN_INPUT_PULLUP 1
#define FUN_INPUT_PULLDOWN 0

#define funInputPullUpDown( pin, mode ) { GpioOf( pin )->OUTDR = (GpioOf( pin )->OUTDR & ~(1 << (pin & 0xf))) | (mode << (pin & 0xf)); }

It can be used like this:

// configure a pin (PC5 in this case) into an input that uses pullup/down 
funPinMode(PC5, GPIO_Speed_In | GPIO_CNF_IN_PUPD);

// actually enable the pullup
funInputPullUpDown(PC5, FUN_INPUT_PULLUP);

...
// read the state
funDigitalRead(PC5);

I've opened this issue to share this as I thought it might come in handy. If it looks like something that could be added to ch32v003fun.h, I'll be glad to send a PR.

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On a tangent, I ordered a bunch of boards for those encoders which turned up today, and they just work because of ch32v003fun. Thank you cnlohr and other contributors for making such a useful project!