msp430_common/include: fix FLASHPAGE definitions
msp430_common/include: fix FLASHPAGE definitions

- TI documentation for msp430f1xx is ambiguous regarding length
  of some memmory sectors. For some cpu's the acual size is 1/4 byte
  smaller than advertised and one of the sectors is actually 256b and
  not 512.
  ref: https://e2e.ti.com/support/microcontrollers/msp430/f/166/p/798838/2962979#2962979
- Remove the first 256b sector from usage since there is not support for
  variable sized pages
- Fix msp430f2617 FLASHPAGE_NUMOFF to represent accesible memory

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