The lock/unlock code is broken beyond repair.

First of all the algorithm doesn't work properly. SPI NOR flashes
can only protect a certain amount of blocks from the end of the device
which is incompatible to the protect(start,len) API we have. The
algorithm tries to be clever by doing protection only when it does
not protect unrelated blocks and unprotection only when it does not
unprotect unrelated blocks. This breaks for example when some code
protects the last blocks (which may contain the bootloader), then
protects the blocks before the last ones (which may contain the
environment). Then if we try to overwrite the bootloader this won't
work since it would unprotect the environment aswell, so the driver
will not unprotect anything resulting in a failed erase/write later.

Then the protection behaviour is different between different flashes.
Some have three protection bits, some have four. For some the smallest
protection are is 1/16 of the device, others have 1/256 or 1/64. Some
have a bit which selects the lower area instead of upper area for
protection. The position of this bit differs on different flashes.

This patch removes the lock code completely and always unprotects
the whole device. This way we can unprotect a device for writing to
it and never protect it again.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>