RFC: Native implementation of WCH two wire procotol

[mean00]

Hi, finally had a bit of time:
This is a request for comment regarding the native support of the two wire protocol / rvswdp as used on WCH chips
(at least CH32V1xx/CH32V2xx/CH32V3XX). As far as i could tell it's not present in the current bmp codebase.
I've been using another flavor of that implementaion for a couple of years and afaik without major issues.

It is piggybacking a bit on the SWD implementation by reusing the SWDIO and SWCLK pins.
To avoid duplication a swdptap_common.h file contain the small common part .

I'm fairly sure the integration with the build system and meson setup is not complete.
I've also created a new target for testing cross/swlink-riscv.ini

In short, it implements the rvswd_scan command in native mode, on top of the work done by @perigoso for the wch-link.

Known Limitation/ things that will be reverted when everything else is okay :
1- the CH32 chips will work up to ~ 1.6Mbit/s only.
2- the errors are not necessarily managed correctly, but it seems "good enough"
4- I added temporarily a nop in the loop clock_on/clock_off macro for debug purpose . Those macros are there for readibility sake, i know they are not necessarily loved.
5- i had to change a bit the swlink platform temporarily to suit my test env, please ignore these changes
6- the implementation is very straightforward and use partially reverse engineered information , probably incomplete

Tested with a CH32V307, output is :

Explain the details for making this change.

• Is a new feature implemented? Yes
• What existing problem(s) does the pull request solve? Native support of WCH protocol for CH32V1/2/3xx
• How does the pull request solve these problems? Implement protocol

Your checklist for this pull request

• I've read the Code of Conduct
• I've read the guidelines for contributing to this repository
• It builds for hardware native (see Building the firmware)
• It builds as BMDA (see Building the BMDA)
• I've tested it to the best of my ability
• My commit messages provide a useful short description of what the commits do

Closing issues