stm32f4/Makefile.include: add riotboot requirements
stm32f4/Makefile.include: add riotboot requirements

- Stm32f4 use sectors instead of pages. They go from 16 KB to 128KB.
  The bootloader will use the first sector(16Kb). Slots must start
  at the begining of a sector to not overlap.
- Minimum required RIOBOOT_HDR_LEN or stm32f4 is 0x200
  to respect vector table alignment

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