stm32_common/flashpage: use HSI only for stm32f0/1
stm32_common/flashpage: use HSI only for stm32f0/1

- Before, HSI was enabled as the default case when it is only
  used for stm32f0 and stm32f1. It is now implemented explicitly
  for those platforms, and only those.

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