boards/{blue,black}pill: Fixed flashing
boards/{blue,black}pill: Fixed flashing

A new blue pill variant with only 32 KiB of flash (secretly coming with
64 KiB flash) instead of the use 64 KiB flash (secretly coming with 128 KiB)
is not compatible with `make flash`. This commit changes the OpenOCD config
so that both variants can be flashed.

mtausig/RIOT,kYc0o/RIOT,RIOT-OS/RIOT,miri64/RIOT,kYc0o/RIOT,kaspar030/RIOT,x3ro/RIOT,ant9000/RIOT,kaspar030/RIOT,OlegHahm/RIOT,authmillenon/RIOT,josephnoir/RIOT,yogo1212/RIOT,basilfx/RIOT,toonst/RIOT,yogo1212/RIOT,cladmi/RIOT,toonst/RIOT,josephnoir/RIOT,aeneby/RIOT,ant9000/RIOT,mtausig/RIOT,jasonatran/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,yogo1212/RIOT,kaspar030/RIOT,OTAkeys/RIOT,rfuentess/RIOT,basilfx/RIOT,authmillenon/RIOT,kYc0o/RIOT,aeneby/RIOT,rfuentess/RIOT,x3ro/RIOT,jasonatran/RIOT,josephnoir/RIOT,miri64/RIOT,smlng/RIOT,toonst/RIOT,rfuentess/RIOT,RIOT-OS/RIOT,miri64/RIOT,basilfx/RIOT,toonst/RIOT,yogo1212/RIOT,kaspar030/RIOT,basilfx/RIOT,yogo1212/RIOT,x3ro/RIOT,yogo1212/RIOT,smlng/RIOT,josephnoir/RIOT,rfuentess/RIOT,cladmi/RIOT,ant9000/RIOT,OlegHahm/RIOT,x3ro/RIOT,x3ro/RIOT,mtausig/RIOT,cladmi/RIOT,authmillenon/RIOT,kYc0o/RIOT,kYc0o/RIOT,RIOT-OS/RIOT,aeneby/RIOT,cladmi/RIOT,josephnoir/RIOT,rfuentess/RIOT,ant9000/RIOT,smlng/RIOT,jasonatran/RIOT,aeneby/RIOT,OlegHahm/RIOT,OTAkeys/RIOT,smlng/RIOT,mtausig/RIOT,authmillenon/RIOT,jasonatran/RIOT,miri64/RIOT,OTAkeys/RIOT,jasonatran/RIOT,OTAkeys/RIOT,miri64/RIOT,mtausig/RIOT,cladmi/RIOT,authmillenon/RIOT,ant9000/RIOT,toonst/RIOT,OlegHahm/RIOT,OlegHahm/RIOT,smlng/RIOT,RIOT-OS/RIOT,OTAkeys/RIOT,basilfx/RIOT,authmillenon/RIOT,aeneby/RIOT