Some supported flash devices (e.g. SST25VF040) are write protected after
power up. If the device holds a valid firmware image the i210 can handle
that just fine. If however there is no firmware programmed, a procedure
is needed to remove this protection before an image can be flashed.

So implement the needed callbacks to make the commands protect and
unprotect do the right thing.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>