SW breakpoint for the CH32V203 (and similar)

The WCH doc clearly states the QingKev4 b does not have hardware breakpoints. We saw that a bit earlier. The CH32V203 among others is a QingKeV4 b . I've added support for flash software breakpoint for the CH32V[2/3]xx to swindle. It is still a bit experimental. When such software breakpoints are used, under the hood the following happens : - Identify the page where the breakpoint is ( 256 bytes…