tmimsp family: flash is now working

The AT25DF family, on power up or reset (not reset of the board, but the
AT25DF part itself) has by default write protection active for its
sectors.  This code change in MotePlatformC for both parts in the family
globally unprotects all sectors.  At this point, the AT25DF family are
functionally equivalent to the ST/Numonyx/whomever M25P family, so the
latter's driver works for the former.