The AT49BV6416 is locked by default, so we really need to provide
at least the unlock() operation for write and erase to work. This
patch implements both ->lock() and ->unlock() and provides a fixup
to install them when an AT49BV6416 chip is detected.

These functions are probably valid on more Atmel chips, but I believe
it's mostly obsolete ones. The AT49BV6416 is in fact obsolete, but
it's used on all current AT32STK1000 development boards.
Signed-off-by: NHaavard Skinnemoen <hskinnemoen@atmel.com>
Signed-off-by: NJosh Boyer <jwboyer@gmail.com>