Add STM32G0316-DISCO

[DurandA]

This PR adds the STM32G0316-DISCO variant which is based on a STM32G0 in SO8 package.

Fix #858. This is a draft PR as I want to gather some feedback from the maintainers first.

[DurandA]

Hi @fpistm, I have a few questions before the PR is ready (and I need to test it properly):

• How is is used .node from boards.txt? What value should I use for Disco.menu.pnum.DISCO_G0316.node?
• As discussed in [New Variant] STM32G0316-DISCO #858, there is no serial line that goes to the ST-Link in this board. It requires to connect an external serial adapter in order to use USART1 (which is the only UART interface in this MCU except LPUART1 but no RX pin is available on the STM32G031J6 for LPUART1). Is it preferred to completely remove Serial definitions in variant.h?

[DurandA]

Hi @fpistm, thank you for your patch.

There were many fixes! One of the issues I had is that I misunderstood the comment All pins are digital, analog inputs are a subset of digital pins. from variant.h of the board_template. I interpreted it as analogInputPin[] is a subset of digitalPin[] so I thought that analogInputPin[] contained indices from digitalPin[], or the starting index of digitalPin[] if NUM_ANALOG_FIRST was used.

I will do some testing in the next few days so you can merge this. If you already tested it and you think it is ready to merge, I marked the PR as ready for review.

Many thanks!

[fpistm]

Hi @DurandA
I close this one as too much conflict.
I've made a new one with pin remap handling: #913